How Do I use the CEA customs on reach?

Just wondering but how do I use the CEA customs. Like the weaker Armor lock and 3 shot pistol? Or the flames that come out your feet with over shield or the actual active camo

how do I turn that on in customs

After playing a matchmaking variant of that game, you can hit start, go to the File Browser> Temporary History> Gametypes, and save them.

Anniversary is the only one to feature the 3-shot Pistol, and is found in Anniversary Classic and BTB playlists.

TU gametypes feature everything but the buffed Pistol, those gametypes are in every playlist but Infection, Anniversary Classic, Team Snipers, Team SWAT, Action Sack, and Squad DLC.
The gametypes are denoted by having a TU prefix before the name of the gametype.

Firefight does not feature the Title Update changes.

To activate the flaming feet, find the Super Shields option in gametype settings.