diff --git a/ckanext/transmute/schema.py b/ckanext/transmute/schema.py
index 1ed38fa..3c9372c 100644
--- a/ckanext/transmute/schema.py
+++ b/ckanext/transmute/schema.py
@@ -63,12 +63,7 @@ def get_replace_from(self) -> Union[list[str], str]:
 
         return self._get_sibling_field_name(self.replace_from)
 
-    def _get_sibling_field_name(self, field_name: str) -> Optional[Any]:
-        field = self.definition["fields"].get(field_name)
-
-        if not field:
-            raise SchemaFieldError(f"Field: sibling field is not exists: {field_name}")
-
+    def _get_sibling_field_name(self, field_name: str) -> str:
         return field_name
 
 
diff --git a/ckanext/transmute/transmutators.py b/ckanext/transmute/transmutators.py
index 04b66c2..5475637 100644
--- a/ckanext/transmute/transmutators.py
+++ b/ckanext/transmute/transmutators.py
@@ -10,7 +10,7 @@
 from ckanext.transmute.types import Field
 
 _transmutators: dict[str, Callable[..., Any]] = {}
-
+SENTINEL = object()
 
 def get_transmutators():
     return _transmutators
@@ -288,3 +288,27 @@ def list_mapper(
     field.value = result
 
     return field
+
+@transmutator
+def map_value(
+    field: Field,
+    test_value: Any,
+    if_same: Any,
+    if_different: Any = SENTINEL,
+) -> Field:
+    """Replace value with other value.
+
+    Args:
+        field: Field object
+        test_value: value that will be compared to field value
+        if_same: value to use if test_value matches the field value
+        if_different: value to use if test_value does not matche the field value.
+            Leave empty to keep original value of the field.
+    """
+    if field.value == test_value:
+        field.value = if_same
+
+    elif if_different is not SENTINEL:
+        field.value = if_different
+
+    return field