Have only tried the cheat with one level whilst online and can confirm that it did give the achievement in respect of finishing the level. Dont want to risk it on the whole game though.
BTW great work on the trainer
Remember, the option works on your RESERVE weapon, not your active weapon. Make sure you have a weapon that overheats in your reserve, activate the option then switch to that weapon and it should work fine. Works for me.
Microsoft Vista checks nearly every program when you are running it. I do know when maybe every 30 minutes. Its a quite annoying feature but if you turn it off Vista and Halo 2 and other related Microsoft products stop working.
It does get kinda annoying saying "Yes" and "Allow" every time you start something.