No standard rules as such, apart from the "out of game" cheats like reloading and loading in SP mode (now fixed in 1.22).
I will try to night to get it done, last night was too hectic for civ...
Apart from restarts for balance issues (which we haven't had for a while), IIRC we have never had a dispute that couldn't be solved with the players. However, the map makers can judge for us if required.
FWIW I keep all my saves (160Gb hard drive
), but you can delete them if you wish. On rare occasions we come across a trade bug that requires going back a few turns, but if I have the saves that would be enough to go back. (IIRC we have had this in maybe 5% of games).