Qubes does not have a built-in snapshot capability like VirtualBox that
can completely revert all changes back to a particular VM state.
Probably not useful for most users since it is getting geeky but I hope I am wrong. However, may be interesting for advanced users...
I am using git to be able to revert back more than to the previous (not last) state of a template. Someone added a while ago here a suggestion to SVN (when you click
expand) since that as the contributor added works better than git for binary files such as VM images.
Git works but it is awfully slow on huge (any Qubes) VM images. But perhaps someone wants to discover / document git / SVN. Would also be interesting to find out if (much more modern and imo usable) git can be tweaked to become efficient on binary files. (We don't have to share these images. Just looking for a hack to record / roll back to past template states.
(That is useful when a Qubes upgrade bug breaks booting the template or during development to test in-place upgrades.)