MonoBehaviourScriptReplacer.cs

public static class MonoBehaviourExtensions
{
#if UNITY_EDITOR

    // [UnityEditor.MenuItem("CONTEXT/MonoBehaviour/Change Script")]
    // [UnityEditor.MenuItem("CONTEXT/AVGFramework.Runtime.UI.AVGImage/Change Script")]
    [UnityEditor.MenuItem("CONTEXT/AVGImage/Change Script")]
    public static void ChangeScript(MenuCommand command)
    {
        if (command.context == null) return;

        var monoBehaviour = command.context as MonoBehaviour;
        var monoScript = MonoScript.FromMonoBehaviour(monoBehaviour);

        var scriptPath = AssetDatabase.GetAssetPath(monoScript);
        var directoryPath = new FileInfo(scriptPath).Directory?.FullName;

        // Allow the user to select which script to replace with
        var newScriptPath = EditorUtility.OpenFilePanel("Select replacement script", directoryPath, "cs");
        newScriptPath = newScriptPath.Replace('\\', '/');

        // Don't log anything if they cancelled the window
        if (string.IsNullOrEmpty(newScriptPath)) return;

        // Load the selected asset
        var relativePath = newScriptPath.Replace(Application.dataPath.Replace("Assets", ""), "");//"Assets\\" + Path.GetRelativePath(Application.dataPath, newScriptPath);
        Debug.Log("newScriptPath: " + relativePath);
        // var chosenTextAsset = AssetDatabase.LoadAssetAtPath<TextAsset>(relativePath);
        var chosenTextAsset = AssetDatabase.LoadAssetAtPath(relativePath, typeof(Object));

        if (chosenTextAsset == null)
        {
            Debug.LogWarning($"Selected script couldn't be loaded ({relativePath})");
            return;
        }

        Undo.RegisterCompleteObjectUndo(command.context, "Changing component script");

        var so = new SerializedObject(monoBehaviour);
        var scriptProperty = so.FindProperty("m_Script");
        so.Update();
        scriptProperty.objectReferenceValue = chosenTextAsset;
        so.ApplyModifiedProperties();
    }

#endif
}