When modifying serialized data through custom editor scripts, it is crucial to interact with the data through SerializedObject and SerializedProperty rather than directly casting the target object. Directly casting the target and modifying its fields only affects an in-memory copy of your script, which does not persist changes to the scene or asset file, leading to data loss upon entering Play Mode. This approach also bypasses the built-in undo/redo system.

To correctly persist changes and enable undo functionality, the custom editor must utilize the serializedObject property of the Editor class:

1. Call serializedObject.Update() to synchronize the SerializedObject with the current state of the target.
2. Access the specific serialized list field as a SerializedProperty using serializedObject.FindProperty("fieldName").
3. Perform all modifications, such as clearing elements or adding new ones, directly on this SerializedProperty using methods like InsertArrayElementAtIndex().
4. Invoke serializedObject.ApplyModifiedProperties() to write the modified values back to the actual serialized object.

Additional Tips:

• Using SerializedProperty automatically handles EditorUtility.SetDirty and allows the Undo system to track changes without manual RecordObject calls.
• For nested classes, ensure you use FindPropertyRelative when accessing fields inside a SerializedProperty element.
• Avoid using AssetDatabase.SaveAssets() for scene-based changes as it triggers a full project re-serialization which is expensive and unnecessary.