diff --git a/capellambse/decl.py b/capellambse/decl.py
index 5410bf26b..f4e2bb37d 100644
--- a/capellambse/decl.py
+++ b/capellambse/decl.py
@@ -240,11 +240,11 @@ def _operate_sync(
     parent: capellambse.ModelObject,
     modifications: dict[str, t.Any],
 ) -> cabc.Generator[_OperatorResult, t.Any, None]:
-    for attr, value in modifications.items():
-        if not isinstance(value, cabc.Iterable):
+    for attr, v in modifications.items():
+        if not isinstance(v, cabc.Iterable):
             raise TypeError("values below `extend:*:` must be lists")
 
-        for obj in value:
+        for obj in v:
             try:
                 find_args = obj.pop("find")
             except KeyError:
@@ -271,8 +271,10 @@ def _operate_sync(
 
             if candidates:
                 candidate = candidates[0]
-                for k, v in obj.pop("set", {}).items():
-                    setattr(candidate, k, v)
+                if mods := obj.pop("set", None):
+                    yield from _operate_modify(promises, candidate, mods)
+                if ext := obj.pop("add", None):
+                    yield from _operate_extend(promises, candidate, ext)
                 promise: str | Promise | None = obj.get("promise_id")
                 if promise is not None:
                     if isinstance(promise, str):
diff --git a/tests/test_decl.py b/tests/test_decl.py
index 555b0d935..db4a24acd 100644
--- a/tests/test_decl.py
+++ b/tests/test_decl.py
@@ -607,6 +607,82 @@ def test_sync_operation_finds_and_modifies_existing_objects_in_the_list(
 
         assert root_function.functions[0].description == new_description
 
+    @staticmethod
+    def test_sync_operation_finds_and_modifies_existing_objects_in_the_list_recurse(
+        model: capellambse.MelodyModel,
+    ) -> None:
+        root_function = model.by_uuid(ROOT_FUNCTION)
+        subfunc = root_function.functions[0]
+        new_input = "Water port"
+        initial_yml = f"""\
+            - parent: !uuid {ROOT_FUNCTION}
+              sync:
+                functions:
+                  - find:
+                      name: {subfunc.name}
+                    set:
+                      inputs:
+                        - name: {new_input}
+            """
+
+        decl.apply(model, io.StringIO(initial_yml))
+        assert new_input in subfunc.inputs.by_name
+        input = "Power port"
+        yml = f"""\
+            - parent: !uuid {ROOT_FUNCTION}
+              sync:
+                functions:
+                  - find:
+                      name: {root_function.functions[0].name}
+                    set:
+                      inputs:
+                        - name: {input}
+            """
+
+        decl.apply(model, io.StringIO(yml))
+        assert (
+            input in subfunc.inputs.by_name
+            and new_input not in subfunc.inputs.by_name
+        )
+
+    @staticmethod
+    def test_sync_operation_finds_and_extends_existing_objects_in_the_list_recurse(
+        model: capellambse.MelodyModel,
+    ) -> None:
+        root_function = model.by_uuid(ROOT_FUNCTION)
+        subfunc = root_function.functions[0]
+        new_input = "Water port"
+        initial_yml = f"""\
+            - parent: !uuid {ROOT_FUNCTION}
+              sync:
+                functions:
+                  - find:
+                      name: {subfunc.name}
+                    add:
+                      inputs:
+                        - name: {new_input}
+            """
+
+        decl.apply(model, io.StringIO(initial_yml))
+        assert new_input in subfunc.inputs.by_name
+        input = "Power port"
+        yml = f"""\
+            - parent: !uuid {ROOT_FUNCTION}
+              sync:
+                functions:
+                  - find:
+                      name: {root_function.functions[0].name}
+                    add:
+                      inputs:
+                        - name: {input}
+            """
+
+        decl.apply(model, io.StringIO(yml))
+        assert (
+            input in subfunc.inputs.by_name
+            and new_input in subfunc.inputs.by_name
+        )
+
     @staticmethod
     def test_sync_operation_creates_a_new_object_if_it_didnt_find_a_match(
         model: capellambse.MelodyModel,