import unreal

OLD = unreal.load_asset("/Game/ImportedAssets/Trees/SM_tree04.SM_tree04")
NEW = unreal.load_asset("/Game/ImportedAssets/Trees/SM_tree01.SM_tree01")

sub = unreal.get_editor_subsystem(unreal.EditorActorSubsystem)
actors = sub.get_all_level_actors()

old_mesh_count = 0

with unreal.ScopedEditorTransaction("Swap meshes"):
    for actor in actors:
        comp = actor.get_component_by_class(unreal.StaticMeshComponent)
        if comp and comp.static_mesh == OLD:
            comp.set_editor_property("static_mesh", NEW)
            # comp.set_static_mesh(NEW) -- tak tez mozna ale undo nie zadziala bo zmiana nie jest robiona przez edytor wiec jej on nie rejestruje
            old_mesh_count += 1

unreal.log(f"Swapped {old_mesh_count} meshes")