Achievements and save editing are a somewhat different matter.
As for catching you MS have been hard on cheating for many years now (the console revocation list actually being in practice way before even DVD hacking really took off in a big way). Depending upon how you sign your save you could get seen, depending upon your edits you could get seen and it need not even be silly although that would just be making their life easier, just something impossible in the general game and frankly if you are going to put the time in to work that out just grind like every other poor bastard that plays such a game.
If you have an offline console cheat away. If you must do it on a console that someone cares about Live for do it offline, do it for an offline profile that you will delete as soon as you get bored and do not cheat hard and even then when the banhammer swings your way "I told you so and here is how to get files off the drive and set up a new box" is about the best you can hope for from those around here or indeed anywhere.