diff --git a/core/chains/evm/config/toml/defaults.go b/core/chains/evm/config/toml/defaults.go
index c3f087da8c5..4e1ebfb34df 100644
--- a/core/chains/evm/config/toml/defaults.go
+++ b/core/chains/evm/config/toml/defaults.go
@@ -3,7 +3,10 @@ package toml
 import (
 	"bytes"
 	"embed"
+	"fmt"
+	"io"
 	"log"
+	"os"
 	"path/filepath"
 	"slices"
 	"strings"
@@ -12,37 +15,43 @@ import (
 
 	"github.com/smartcontractkit/chainlink/v2/core/chains/evm/config/chaintype"
 	"github.com/smartcontractkit/chainlink/v2/core/chains/evm/utils/big"
+	"github.com/smartcontractkit/chainlink/v2/core/config/env"
 )
 
 var (
+
 	//go:embed defaults/*.toml
 	defaultsFS   embed.FS
 	fallback     Chain
 	defaults     = map[string]Chain{}
 	defaultNames = map[string]string{}
 
+	customDefaults = map[string]Chain{}
+
 	// DefaultIDs is the set of chain ids which have defaults.
 	DefaultIDs []*big.Big
 )
 
 func init() {
+	// read the defaults first
+
 	fes, err := defaultsFS.ReadDir("defaults")
 	if err != nil {
 		log.Fatalf("failed to read defaults/: %v", err)
 	}
 	for _, fe := range fes {
 		path := filepath.Join("defaults", fe.Name())
-		b, err := defaultsFS.ReadFile(path)
-		if err != nil {
-			log.Fatalf("failed to read %q: %v", path, err)
+		b, err2 := defaultsFS.ReadFile(path)
+		if err2 != nil {
+			log.Fatalf("failed to read %q: %v", path, err2)
 		}
 		var config = struct {
 			ChainID *big.Big
 			Chain
 		}{}
 
-		if err := cconfig.DecodeTOML(bytes.NewReader(b), &config); err != nil {
-			log.Fatalf("failed to decode %q: %v", path, err)
+		if err3 := cconfig.DecodeTOML(bytes.NewReader(b), &config); err3 != nil {
+			log.Fatalf("failed to decode %q: %v", path, err3)
 		}
 		if fe.Name() == "fallback.toml" {
 			if config.ChainID != nil {
@@ -65,6 +74,63 @@ func init() {
 	slices.SortFunc(DefaultIDs, func(a, b *big.Big) int {
 		return a.Cmp(b)
 	})
+
+	// read the custom defaults overrides
+	dir := env.CustomDefaults.Get()
+	if dir == "" {
+		// short-circuit; no default overrides provided
+		return
+	}
+
+	// use evm overrides specifically
+	evmDir := fmt.Sprintf("%s/evm", dir)
+
+	// Read directory contents for evm only
+	entries, err := os.ReadDir(evmDir)
+	if err != nil {
+		log.Fatalf("error reading evm custom defaults override directory: %v", err)
+		return
+	}
+
+	for _, entry := range entries {
+		if entry.IsDir() {
+			// Skip directories
+			continue
+		}
+
+		path := evmDir + "/" + entry.Name()
+		file, err := os.Open(path)
+		if err != nil {
+			log.Fatalf("error opening file (name: %v) in custom defaults override directory: %v", entry.Name(), err)
+		}
+
+		// Read file contents
+		b, err := io.ReadAll(file)
+		file.Close()
+		if err != nil {
+			log.Fatalf("error reading file (name: %v) contents in custom defaults override directory: %v", entry.Name(), err)
+		}
+
+		var config = struct {
+			ChainID *big.Big
+			Chain
+		}{}
+
+		if err := cconfig.DecodeTOML(bytes.NewReader(b), &config); err != nil {
+			log.Fatalf("failed to decode %q in custom defaults override directory: %v", path, err)
+		}
+
+		if config.ChainID == nil {
+			log.Fatalf("missing ChainID in: %s in custom defaults override directory. exiting", path)
+		}
+
+		id := config.ChainID.String()
+
+		if _, ok := customDefaults[id]; ok {
+			log.Fatalf("%q contains duplicate ChainID: %s", path, id)
+		}
+		customDefaults[id] = config.Chain
+	}
 }
 
 // DefaultsNamed returns the default Chain values, optionally for the given chainID, as well as a name if the chainID is known.
@@ -78,6 +144,9 @@ func DefaultsNamed(chainID *big.Big) (c Chain, name string) {
 		c.SetFrom(&d)
 		name = defaultNames[s]
 	}
+	if overrides, ok := customDefaults[s]; ok {
+		c.SetFrom(&overrides)
+	}
 	return
 }
 
diff --git a/core/config/env/env.go b/core/config/env/env.go
index 0ebfc357bf3..c34cd7f4f5e 100644
--- a/core/config/env/env.go
+++ b/core/config/env/env.go
@@ -20,6 +20,7 @@ var (
 	ThresholdKeyShare            = Secret("CL_THRESHOLD_KEY_SHARE")
 	// Migrations env vars
 	EVMChainIDNotNullMigration0195 = "CL_EVM_CHAINID_NOT_NULL_MIGRATION_0195"
+	CustomDefaults                 = Var("CL_CHAIN_DEFAULTS")
 )
 
 // LOOPP commands and vars
diff --git a/main_test.go b/main_test.go
index 81e056e3b84..419a4af0517 100644
--- a/main_test.go
+++ b/main_test.go
@@ -42,6 +42,10 @@ func TestMain(m *testing.M) {
 	}))
 }
 
+// TestScripts walks through the testdata/scripts directory and runs all tests that end in
+// .txt or .txtar with the testscripts library. To run an individual test, specify it in the
+// -run param of go test without the txtar or txt suffix, like so:
+// go test . -run TestScripts/node/validate/default
 func TestScripts(t *testing.T) {
 	if testing.Short() {
 		t.Skip("skipping testscript")
diff --git a/testdata/scripts/node/validate/defaults-override.txtar b/testdata/scripts/node/validate/defaults-override.txtar
new file mode 100644
index 00000000000..3accd1584bb
--- /dev/null
+++ b/testdata/scripts/node/validate/defaults-override.txtar
@@ -0,0 +1,444 @@
+# test with default override
+env CL_CHAIN_DEFAULTS=default_overrides
+exec chainlink node -c config.toml -s secrets.toml validate
+cmp stdout out.txt
+
+# remove override, FinalityTagEnabled should no longer match
+env CL_CHAIN_DEFAULTS=
+exec chainlink node -c config.toml -s secrets.toml validate
+! cmp stdout out.txt
+
+# overrides outside of evm suffix, FinalityTagEnabled should not match as override is not applied
+env CL_CHAIN_DEFAULTS=default_overrides2
+! exec chainlink node -c config.toml -s secrets.toml validate
+
+# duplicate chain IDs
+env CL_CHAIN_DEFAULTS=default_overrides3
+! exec chainlink node -c config.toml -s secrets.toml validate
+stderr 'contains duplicate ChainID'
+
+-- default_overrides/evm/Ethereum_Mainnet.toml --
+ChainID = '1'
+FinalityTagEnabled = true
+
+-- default_overrides2/Ethereum_Mainnet.toml --
+ChainID = '1'
+FinalityTagEnabled = true
+
+-- default_overrides3/evm/Ethereum_Mainnet.toml --
+ChainID = '1'
+
+-- default_overrides3/evm/Ethereum_Testnet.toml --
+ChainID = '1'
+
+-- config.toml --
+Log.Level = 'debug'
+
+[[EVM]]
+ChainID = '1'
+
+[[EVM.Nodes]]
+Name = 'fake'
+WSURL = 'wss://foo.bar/ws'
+HTTPURL = 'https://foo.bar'
+
+-- secrets.toml --
+[Database]
+URL = 'postgresql://user:pass1234567890abcd@localhost:5432/dbname?sslmode=disable'
+
+[Password]
+Keystore = 'keystore_pass'
+
+-- out.txt --
+# Secrets:
+[Database]
+URL = 'xxxxx'
+AllowSimplePasswords = false
+
+[Password]
+Keystore = 'xxxxx'
+
+# Input Configuration:
+[Log]
+Level = 'debug'
+
+[[EVM]]
+ChainID = '1'
+
+[[EVM.Nodes]]
+Name = 'fake'
+WSURL = 'wss://foo.bar/ws'
+HTTPURL = 'https://foo.bar'
+
+# Effective Configuration, with defaults applied:
+InsecureFastScrypt = false
+RootDir = '~/.chainlink'
+ShutdownGracePeriod = '5s'
+
+[Feature]
+FeedsManager = true
+LogPoller = false
+UICSAKeys = false
+CCIP = true
+MultiFeedsManagers = false
+
+[Database]
+DefaultIdleInTxSessionTimeout = '1h0m0s'
+DefaultLockTimeout = '15s'
+DefaultQueryTimeout = '10s'
+LogQueries = false
+MaxIdleConns = 10
+MaxOpenConns = 100
+MigrateOnStartup = true
+
+[Database.Backup]
+Dir = ''
+Frequency = '1h0m0s'
+Mode = 'none'
+OnVersionUpgrade = true
+
+[Database.Listener]
+MaxReconnectDuration = '10m0s'
+MinReconnectInterval = '1m0s'
+FallbackPollInterval = '30s'
+
+[Database.Lock]
+Enabled = true
+LeaseDuration = '10s'
+LeaseRefreshInterval = '1s'
+
+[TelemetryIngress]
+UniConn = true
+Logging = false
+BufferSize = 100
+MaxBatchSize = 50
+SendInterval = '500ms'
+SendTimeout = '10s'
+UseBatchSend = true
+
+[AuditLogger]
+Enabled = false
+ForwardToUrl = ''
+JsonWrapperKey = ''
+Headers = []
+
+[Log]
+Level = 'debug'
+JSONConsole = false
+UnixTS = false
+
+[Log.File]
+Dir = ''
+MaxSize = '5.12gb'
+MaxAgeDays = 0
+MaxBackups = 1
+
+[WebServer]
+AuthenticationMethod = 'local'
+AllowOrigins = 'http://localhost:3000,http://localhost:6688'
+BridgeResponseURL = ''
+BridgeCacheTTL = '0s'
+HTTPWriteTimeout = '10s'
+HTTPPort = 6688
+SecureCookies = true
+SessionTimeout = '15m0s'
+SessionReaperExpiration = '240h0m0s'
+HTTPMaxSize = '32.77kb'
+StartTimeout = '15s'
+ListenIP = '0.0.0.0'
+
+[WebServer.LDAP]
+ServerTLS = true
+SessionTimeout = '15m0s'
+QueryTimeout = '2m0s'
+BaseUserAttr = 'uid'
+BaseDN = ''
+UsersDN = 'ou=users'
+GroupsDN = 'ou=groups'
+ActiveAttribute = ''
+ActiveAttributeAllowedValue = ''
+AdminUserGroupCN = 'NodeAdmins'
+EditUserGroupCN = 'NodeEditors'
+RunUserGroupCN = 'NodeRunners'
+ReadUserGroupCN = 'NodeReadOnly'
+UserApiTokenEnabled = false
+UserAPITokenDuration = '240h0m0s'
+UpstreamSyncInterval = '0s'
+UpstreamSyncRateLimit = '2m0s'
+
+[WebServer.MFA]
+RPID = ''
+RPOrigin = ''
+
+[WebServer.RateLimit]
+Authenticated = 1000
+AuthenticatedPeriod = '1m0s'
+Unauthenticated = 5
+UnauthenticatedPeriod = '20s'
+
+[WebServer.TLS]
+CertPath = ''
+ForceRedirect = false
+Host = ''
+HTTPSPort = 6689
+KeyPath = ''
+ListenIP = '0.0.0.0'
+
+[JobPipeline]
+ExternalInitiatorsEnabled = false
+MaxRunDuration = '10m0s'
+MaxSuccessfulRuns = 10000
+ReaperInterval = '1h0m0s'
+ReaperThreshold = '24h0m0s'
+ResultWriteQueueDepth = 100
+VerboseLogging = true
+
+[JobPipeline.HTTPRequest]
+DefaultTimeout = '15s'
+MaxSize = '32.77kb'
+
+[FluxMonitor]
+DefaultTransactionQueueDepth = 1
+SimulateTransactions = false
+
+[OCR2]
+Enabled = false
+ContractConfirmations = 3
+BlockchainTimeout = '20s'
+ContractPollInterval = '1m0s'
+ContractSubscribeInterval = '2m0s'
+ContractTransmitterTransmitTimeout = '10s'
+DatabaseTimeout = '10s'
+KeyBundleID = '0000000000000000000000000000000000000000000000000000000000000000'
+CaptureEATelemetry = false
+CaptureAutomationCustomTelemetry = true
+DefaultTransactionQueueDepth = 1
+SimulateTransactions = false
+TraceLogging = false
+
+[OCR]
+Enabled = false
+ObservationTimeout = '5s'
+BlockchainTimeout = '20s'
+ContractPollInterval = '1m0s'
+ContractSubscribeInterval = '2m0s'
+DefaultTransactionQueueDepth = 1
+KeyBundleID = '0000000000000000000000000000000000000000000000000000000000000000'
+SimulateTransactions = false
+TransmitterAddress = ''
+CaptureEATelemetry = false
+TraceLogging = false
+
+[P2P]
+IncomingMessageBufferSize = 10
+OutgoingMessageBufferSize = 10
+PeerID = ''
+TraceLogging = false
+
+[P2P.V2]
+Enabled = true
+AnnounceAddresses = []
+DefaultBootstrappers = []
+DeltaDial = '15s'
+DeltaReconcile = '1m0s'
+ListenAddresses = []
+
+[Keeper]
+DefaultTransactionQueueDepth = 1
+GasPriceBufferPercent = 20
+GasTipCapBufferPercent = 20
+BaseFeeBufferPercent = 20
+MaxGracePeriod = 100
+TurnLookBack = 1000
+
+[Keeper.Registry]
+CheckGasOverhead = 200000
+PerformGasOverhead = 300000
+MaxPerformDataSize = 5000
+SyncInterval = '30m0s'
+SyncUpkeepQueueSize = 10
+
+[AutoPprof]
+Enabled = false
+ProfileRoot = ''
+PollInterval = '10s'
+GatherDuration = '10s'
+GatherTraceDuration = '5s'
+MaxProfileSize = '100.00mb'
+CPUProfileRate = 1
+MemProfileRate = 1
+BlockProfileRate = 1
+MutexProfileFraction = 1
+MemThreshold = '4.00gb'
+GoroutineThreshold = 5000
+
+[Pyroscope]
+ServerAddress = ''
+Environment = 'mainnet'
+
+[Sentry]
+Debug = false
+DSN = ''
+Environment = ''
+Release = ''
+
+[Insecure]
+DevWebServer = false
+OCRDevelopmentMode = false
+InfiniteDepthQueries = false
+DisableRateLimiting = false
+
+[Tracing]
+Enabled = false
+CollectorTarget = ''
+NodeID = ''
+SamplingRatio = 0.0
+Mode = 'tls'
+TLSCertPath = ''
+
+[Mercury]
+VerboseLogging = false
+
+[Mercury.Cache]
+LatestReportTTL = '1s'
+MaxStaleAge = '1h0m0s'
+LatestReportDeadline = '5s'
+
+[Mercury.TLS]
+CertFile = ''
+
+[Mercury.Transmitter]
+TransmitQueueMaxSize = 10000
+TransmitTimeout = '5s'
+
+[Capabilities]
+[Capabilities.Peering]
+IncomingMessageBufferSize = 10
+OutgoingMessageBufferSize = 10
+PeerID = ''
+TraceLogging = false
+
+[Capabilities.Peering.V2]
+Enabled = false
+AnnounceAddresses = []
+DefaultBootstrappers = []
+DeltaDial = '15s'
+DeltaReconcile = '1m0s'
+ListenAddresses = []
+
+[Capabilities.Dispatcher]
+SupportedVersion = 1
+ReceiverBufferSize = 10000
+
+[Capabilities.Dispatcher.RateLimit]
+GlobalRPS = 800.0
+GlobalBurst = 1000
+PerSenderRPS = 10.0
+PerSenderBurst = 50
+
+[Capabilities.ExternalRegistry]
+Address = ''
+NetworkID = 'evm'
+ChainID = '1'
+
+[[EVM]]
+ChainID = '1'
+AutoCreateKey = true
+BlockBackfillDepth = 10
+BlockBackfillSkip = false
+FinalityDepth = 50
+FinalityTagEnabled = true
+LinkContractAddress = '0x514910771AF9Ca656af840dff83E8264EcF986CA'
+LogBackfillBatchSize = 1000
+LogPollInterval = '15s'
+LogKeepBlocksDepth = 100000
+LogPrunePageSize = 0
+BackupLogPollerBlockDelay = 100
+MinIncomingConfirmations = 3
+MinContractPayment = '0.1 link'
+NonceAutoSync = true
+NoNewHeadsThreshold = '3m0s'
+OperatorFactoryAddress = '0x3E64Cd889482443324F91bFA9c84fE72A511f48A'
+RPCDefaultBatchSize = 250
+RPCBlockQueryDelay = 1
+FinalizedBlockOffset = 0
+NoNewFinalizedHeadsThreshold = '9m0s'
+
+[EVM.Transactions]
+ForwardersEnabled = false
+MaxInFlight = 16
+MaxQueued = 250
+ReaperInterval = '1h0m0s'
+ReaperThreshold = '168h0m0s'
+ResendAfterThreshold = '1m0s'
+
+[EVM.Transactions.AutoPurge]
+Enabled = false
+
+[EVM.BalanceMonitor]
+Enabled = true
+
+[EVM.GasEstimator]
+Mode = 'BlockHistory'
+PriceDefault = '20 gwei'
+PriceMax = '115792089237316195423570985008687907853269984665.640564039457584007913129639935 tether'
+PriceMin = '1 gwei'
+LimitDefault = 500000
+LimitMax = 500000
+LimitMultiplier = '1'
+LimitTransfer = 21000
+EstimateGasLimit = false
+BumpMin = '5 gwei'
+BumpPercent = 20
+BumpThreshold = 3
+EIP1559DynamicFees = true
+FeeCapDefault = '100 gwei'
+TipCapDefault = '1 wei'
+TipCapMin = '1 wei'
+
+[EVM.GasEstimator.BlockHistory]
+BatchSize = 25
+BlockHistorySize = 4
+CheckInclusionBlocks = 12
+CheckInclusionPercentile = 90
+TransactionPercentile = 50
+
+[EVM.HeadTracker]
+HistoryDepth = 100
+MaxBufferSize = 3
+SamplingInterval = '1s'
+MaxAllowedFinalityDepth = 10000
+FinalityTagBypass = true
+
+[EVM.NodePool]
+PollFailureThreshold = 5
+PollInterval = '10s'
+SelectionMode = 'HighestHead'
+SyncThreshold = 5
+LeaseDuration = '0s'
+NodeIsSyncingEnabled = false
+FinalizedBlockPollInterval = '5s'
+EnforceRepeatableRead = false
+DeathDeclarationDelay = '10s'
+
+[EVM.OCR]
+ContractConfirmations = 4
+ContractTransmitterTransmitTimeout = '10s'
+DatabaseTimeout = '10s'
+DeltaCOverride = '168h0m0s'
+DeltaCJitterOverride = '1h0m0s'
+ObservationGracePeriod = '1s'
+
+[EVM.OCR2]
+[EVM.OCR2.Automation]
+GasLimit = 10500000
+
+[EVM.Workflow]
+GasLimitDefault = 400000
+
+[[EVM.Nodes]]
+Name = 'fake'
+WSURL = 'wss://foo.bar/ws'
+HTTPURL = 'https://foo.bar'
+
+Valid configuration.