Depends on the game. Emulators are a thing, but they're not always allowed, you'll have to ask the community of the game you want to run to make sure.

if a crack is required, and said crack modifies or replaces game files the answer is a big fat NOPE. assuming anyone were to find out... though i suppose you just told everyone... otherwise nobody cares outside of emulation, which simply needs to be disclaimed and categorized.

I mean technically you can speedrun anything as much as you like, you just may not be able to have your time on the boards. If the community doesn't allow that version, why not play on it first to see if you like it and then buy a legit copy if you want to go further?