Is it safe to mod 360 gs now and not worry about getting banned?

Let me explain, I no longer have access to my xbl account from when the 360 first came out. A lot of the achievements I got are no longer obtainable. I merely want to get those achievements through modding and then continue getting modern day games legit. Am I safe or will this eventually result in the account being banned? Asking because I plan to buy stuff on the account and i’d rather not waste money if i’m just gonna lose it. Thanks for any help!! (yes i’m willing to individually go through and change the times/dates of when I originally unlocked them)