Make all the changes you like
Go into the folder where Re-Volt is installed. There should be another folder named 'cars'. In here, every car in the game (with the exception of secret cars) has it's own folder, each containing a text file called 'Parameters'. By editing this file, you can choose how fast, how big etc you want the corresponding car to be. You can even change how grippy the tires are and how much the cars weigh.

Tiny cars
Enter DRINKME as your name

Unlock all cars
Enter CARNIVAL as your name

Unlock all tracks
Enter TRACKER as your name

Unlock flying UFO
Enter URCO as your name

View select
Enter TVTIME as your name (F5 and F6 changes the view)