I think you press up or down on the D-pad. But you have to be in Forge. To go back to normal you press the same button
If your talking about the orical, then just press up on the D-pad to change back and forth between your player and the orical.
you can customize your character in halo 3. and you can change your character that has different armor in halo 3:odst
It's a little bit longer than halo 3
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.
If you mean the monitor on halo 3 forge then no, you cannot make the monitor use a laser. Only the monitor from the campaign (343 guilty spark) can use its laser, which it will do when prevoked.
Yes a little
Technically no, the only way to wear armor in halo 3 that you can wear in reach is some of the basic armor that was already available but the new pieces of armor such as the security shoulders, sapper chest with robot arm, an gungir helmet are only available in Reach.
go .... yourself in the menu
In your multiplayer settings.