Yes, yes and yes.
Although a backup is recommended.
Also what I tend to do when testing is keep all my test version tar files in /storage, then I can ssh in and copy the version I want to test to .update and reboot to install it. If I want to revert, it is easy to copy the old version tar file to .update and reboot again.
Of course now with LE it works with .img.gz files too.