So I've beaten the game and earned nearly all achievements, and I'm about to do what I usually do with a SR game: Cheat it on a new file.
I found an official list, but a very large portion of the cheats are not recognized by the game.
I've heard somewhere that they're unlocked. I haven't completed all of the Challenges, so I can only venture a guess as this is how it's done.
Here's the list: www.gamespot.com/saints-row-iv/cheats/
Note: I am on Xbox, and am really only wanting to hack in the rare vehicles that I couldn't obtain in SR:TT.