Modify the Windows shortcut to the game (TTT.exe) and add the following command-line parameters for the corresponding cheat function:
Parameter Result
-? Help
-codename:laamanen007 Limo Bonuscar
-accs Access All Tracks and Shadow Tracks

Example of Above: "c:\Thrust\TTT.exe -accs" (for access to all tracks)

You can also edit the car*.sto, and limo.sto file(s) to suit your needs.