Unfortunately AGMaker doesn’t have that option because it runs on Godot, and Godot saves the project every time you playtest.
アクションゲームツクールMV could do it because the playtest ran off a separate file. The project lived in project.json and the playtest wrote to test.json, so with that setting off, only test.json got updated. If you didn’t like how an experiment turned out, you could quit without saving and the project was untouched. In AGMaker the playtest works from the project itself, so every playtest saves your changes along with it.
It’s not so much that it’s an alternative, but since the Undo function is more robust in Action Game Tsukuru MV than in others, it might be better to test play and use Undo to go back if things don’t go well.