The rule could be anything, as funny or as serious as you want. The universe will progress in a similar way that it has up until this point, unless your changed rule prevented it from doing so.
Some examples might be:
- The invention of currency is not allowed.
- Iron is slightly less stable.
- The Ancient Greeks are able to cultivate Silphium, which does not go extinct now.
What if it is an accident? Do both parties just get erased from the universe? Or is all malice just gone from the human will?
No, it’s more like
"teamplay": 1; "coop": 1;and then you punt your buddies into lava with the rocketlauncher.