Here we go.

XP to stick*
1. Say your at rank 50, ok now prestige.
2. Press B Then click Main menu.
3. Go back to Multiplayer.
4. Click Xbox Live.
5. You would now be back to level 50
6. Prestige again.
7. The rank should now stick.

Get Cod Points to stick* (Credits to GoldReaper300)
1. When you are at your desired prestige.
2. Once you are level 1 (whatever prestige) get back into a lobby.
3. Kill yourself until you are level 50 and positive COD Points( press SELECT button, hover over your gamertag, and press Y)
4. It will change every time you kill yourself.
5. It will take over 20 times (Yes, your k/d will go down)
6. When you are done it will typically say Level 50 with positive 9,900,000 COD points.
7. Wait until the hosts leave and you are the host and leave.
8. Sign out and sign in (if you did it right, it will stick)
10. Buy anything your heart desires.
11. Don't search for those Team Tactical matches because if you kill yourself even once, you will have to start these steps over again and all your purchases will be lost

Note: Sorry, if this has been posted multiple time.
Just wanted to clear this up so we don't have any spam topics on how to make things stick.