Can I Undo the Changes if Something Goes Wrong?
Yes, because your original export is never altered. Here is how the safety works.
Yes, and the way it works is simpler than an undo button: your original is never touched.
The app reads your Takeout export and writes a corrected library into a different folder that you choose. The export stays exactly as Google delivered it. If you dislike the result, delete the new folder and run it again with different settings. Nothing is lost because nothing was changed. If you ask it to tidy a folder in place instead, it can keep untouched copies of everything before it starts.
There is also a preview that shows every new name, every folder and every date change before a single file is written. Use it once on a folder you know well and you will see exactly what the real run will do. The first 500 photos are free, so the whole thing can be tested at no cost.