It's not a Downlaod. They work in forge only though so no game cheating.
But you'll need to practice the Armor lock cheat and the Hologram cheat.
Have either one equipped. and when you activate them, you'll want to hit your editor button as soon as you activate. It's all about the timing and you'll need another person with you when performing these, I don't think they work when you're by yourself.
The Armor Lock makes you completely invincible, even to tossing vehicles with you in it, but not to Take Down moves, or drowning.
And the Hologram will display a different Spartan each time you use it.
I just did it for fun, It was another 405th member who showed me. I'm on XBL right now in Forge if you'd like to join me. and you can practice, if those're what you're looking for.