Well what aspect of the game are you editing? You can add kits with kit-raptor 2, thats pretty safe, install balls manually, using big raptor, avoid ballrev, install boots manually, and remember to run fat-bh builder. If you edit the database, make sure the data is not illegal, for example, make sure the values are within the range allowed (like boots for example 1-9,, kits 1-6 etc.) Make sure all the data exist for a player and team and everything adds up logically, if you screw up fifa.db, you'll have a CTD almost after every game. And remember, back up all files before editing!!!