I know the first person cheat is okay, but what about other achievements.

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The Great Legend
GoW & GoW 2 Hall of Famer

Most of the cheats disable the achievements and saving progress.

They all disable achievements/level ups...well at least the ones Ive tried like the invincibility one, unlimited melee weapons, and where all the items are in the game setting. Sucks...but I use the invincibility cheat to try out a boss first and see what makes him tick before I go into it for 'real'.