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.
I believe both. Fusion bomb was made after the fission one. So ya, that’s a tough one.
But I suppose as long as we’re just making wishes, there’s got to be one like things can’t explode but you can still get harmless energy from them or something like that, so stars still work. Idk,this one might require a physicist to phrase it right lol.