Here are a few steps you can follow to make your account with modded achievements look more legit.

1. Time Stamp legitly.
-Yes, time stamping in general is a good start, but you have to do a little bit more work. If you just go and unlock all the Call of Duty Veteran achievements all in a row, there is a difference by seconds in the time stamp. Does Microsoft really think you beat the whole CoD campaign in 2 minutes? No...
- To make this look better, take the time to spread out the dates and times. Unlock one achievement, and for the next, make the time stamp the next hour or so. Complete this following the same principle.

2. Gamer Score Display is Unreliable
-If you haven't noticed already, check your gamer score. On your Dashboard, you might have 5,150. But then if you check your gamer score on your games history, it might show 5,179. Also, if you compare games with a friend, you might see your gamer score depicted as 5,924.

Also, if you mod your achievements using Xbox 360 Profile Editor, you will only see pictures for the achievements you unlocked legit. The ones you all modded have no picture.

Then, when you save your profile, you should of noticed that your profile doesn't get any bigger, even when modding 1,000 achievements...

THE FIX:

Simply recover your account! It may take longer than usual now, if you have unlocked a lot of achievements, seeing as it downloads the pictures of the achievements and other various things into your account.

After your done recovering, you should notice that when your on the dashboard, comparing games, and looking at game history, that your gamer score is all the same.

Also, if you open up your profile in Xbox 360 Profile Editor, you will see all the pictures off all the achievements you have unlocked, even the modded ones.

Also, look at your profile. It's size has increased!

In the end, this should make it harder for Microsoft to notice that you have been modding your gamer score and giving you a better chance that your gamer score won't be reset.