How Can I Disable Cheats?

[SpecialistWafer]

I bought the game a while ago, and I made the mistake of letting my ♥♥♥♥♥♥♥ brother play it. He decided to f*** with me by entering the cheat that unlocks all the missions from the get-go. Anyone know how to reset my game in such a way as to disable that cheat so I can play through the campaigns properly? I've tried uninstalling the game then reinstalling it, but that didn't work. I also attempted a re-input of the cheat, since that typically disables them in other games.