I've ruined so many games with "god mode" hacks that way. Even something like giving the player obscene amounts of currency and continuing the play the game "as normal" afterward slowly killed it.

So, I save that kind of thing for _after_ the 100% mark (or even 90% for some). When I'm done going as far as I plan to go, then I open up the hacks and mods and see what craziness awaits.