you click the start button, then you press right on the d-pad, then go to appearance and there you go...
You can just change your colours and try to look like them OR you can keep on leveling and unlock their amour.
i found it on a legit map only wich i think is the only way
you can customize your character in halo 3. and you can change your character that has different armor in halo 3:odst
If You Mean change into elite, no, you can only do that in Halo 2, 3 and Halo Reach. But however you can use mods at halomods.com
No
Yes, halo 3 mythic is the exact same thing as halo 3 just doesn't have the campaign, also Halo 3 mythic has the new mythic maps included. Online will not change during any gameplay.
You have to put in the Mythic disc, then its the same way as Halo 3.
go .... yourself in the menu
In your multiplayer settings.
play sonic in halo just download and the maps change
Halo 3 I'm guessing Start, Right, Down, A. That'll give you the ability to change your color, armor, emblem etc.
You can't. The game has been released and there will be no changing.