Pretty much what I can't do is anything to do with changing the physical map, like inserting another base or something like that, or I can't change the physical appearance of the characters, like making Master Cheif taller, or something.
Another thing that I have done is made the Carbine shoot Master Cheifs, so you can make a group of them, then hide in the middle of them so noone can tell which one is the real you. All of the other mastercheifs just stand there, and if you throw a grenade into the middle all of their bodies go flying half way across the map
I still haven't gotten the new maps, but I am planning on getting them soon. Once you put the new maps on you can't do most of the glitches anymore, like the rocket-sword one, but If I really want to do them I could just take the new maps off again.
And about the handgun that you were talking about before, I can put up to 3 zooms, 1x probably all the way up to 999x, although I haven't tried it, since that would be kind of hard so see what you are aiming at. I could also make it do more damage, if the Magnum does less than in Halo 1.