You may be thinking too big...
Like previous posters, I agree that designing your own ride vehicle would be a mess.
My guess is that this is a new generation interactive queue, much like Soarin' or Space Mountain. In the standby line, you will have the ability to design a car along the way at various stations.
Enter the briefing room and you'll see the cars that have been designed by those in the line, rather than the 1990's era cars in the current video. Heck, they could take your picture along the way and you could be in the car, waving. (Think SSE.)
The ride vehicles will likely be updated. They may even figure out a way to have the car's screen show your design running through the tests. The video displays along the route could also overlay your design on the ride vehicle in a replay.
By the way, this could be very simple to pull off with RFID enabled admission media.