Can I undo a change or go back to an earlier version?

Yes. Every single change carries its own Undo, both in the chat thread and in the list of pending changes. There is also a restore point for each day, if you would rather put the whole site back to how it was.

Restoring is safe: it brings that day's version back as a new version rather than overwriting anything, so you can always go forward again. Because every version is kept, it is very hard to truly break your site, and if you ever get stuck our team can restore it for you.