Not technically illegal, however it is in breach of their 'Terms of Use', definitely ill-advised. They can, and will, ban your account and IP address. If you are gonna mod, do it offline only and don't mod your Gamerscore or credits etc.
Yes especially online modding.
they will fry your 360
you get banned by modding credits instead of earning them yourself
yes there are many programs available like Xport 360
I've seen someone play the campaign as a jackal by modding their game.
OK first that first answer was someone who NEVER! played HALO (WHICH IS AWSOME BY THE WAY!!!) you can't drive one in halo without modding. BUT maybe in Halo Reach you can >: )
Yes
no because bungie disabled offline to online transitions with credits and armors and modding your credits will count as offline credit gaining
You cannot; it is illegal.
You get banned for modding anything dealing with an Xbox
you could buy it or get it illegally halo reach code generator. very very illegal it generates codes
actuelly no.. but you have a 3% chance of becomming one with some searious illegal modding, of corse you can be a hunter in halo 1 PC with some simple downloadable patches and stuff..