*NOTE* dont do too many times, I say more than twice in one day because if you get too many challenges in one day bungie will watch you and will reset everything if you do it too much
*NOTE 2* Doesnt work 100% of the time.
1)First off you need to do all the challenges for the day until you are satisfied.
2) Play one more game after you get the desired challenges (not needed but i do it just to make sure the gane before is in the system)
go to Lobby for Reach via Matchmaking, Firefight, Custom Games,etc and while connected to xbox live, sign out but dont leave the guide yet, go to sign in, WITHOUT leaving the guide and sign into an strictly offline profile, that means no prior xbox live connection or membership. and it will take you to title screen.
4)*Note* not necessarily needed but i do for safe keeping, with the offline profile signed in, start a custom game and play for 5 seconds and quit.
5) From the lobby you just got back to with the online profile press the center button and sign out, once again DONT leave the guide and sign back into your xbox live profile with the challenges you recently acquired.
6) It will take you back to main menu and you check the challenges say you havent done them but you still have the creits and rank progression from before when you got them. For instance today I got 3 challenges in one game, 2 worth 350 and one worth 1200. Add all of the after game stuff and in 3 games i earned over 6000 credits