I'm thinking of a program that has all the standard gametypes stored in a directory (i.e Slayer, CTF etc..) and you select what changes you might want (i.e Respawn times, No Hud, lots of oddballs etc...) and then hit generate. The program would then cough up a modded gametype variant which you would then move to your xbox via ActionReplay.
So.. is there one about? and if not, why not

Cheers.