Here's how he does it with ARmax..
| I use a combination of codes and a glitch. First put your favorite wheels on a moddable car, then park it at the garage in Ganton. Note that this glitch only works with wheels, & nitrous and sometimes hydraullics. If you put any other mods on this car, your game will freeze.|
Then you use the "replace car at cj's garage with..." code, and the color modifier codes for it.
The code replaces the car you parked in the garage with the car you chose with the replace code. A glitch then morphs the mods from the parked car onto the replacement car.