Found by: lm4eversmart4

Tutorial:
1. Go to main menu
2. Send changes to game from elite
3. Go to multiplayer and then to xboxlive to start a lobby
4. Lag switch right when you join the lobby
5. Go into private match and load a game save from your vault
6. Back out to the xbox live lobby
7. Turn off lagswitch
8. Wait for the failed to load custom match appears, then the elite pop up will appear
9. Wait about 1-2 seconds and then accept changes

If you did it right, all of your custom classes will be null. If you did it wrong, its because you clicked too early. If you click too late, a second elite popup will come out. This method might be what TehPoisonOne used to bring modded custom classes online