Ah, that's quite handy indeed. Thanks for that, i'll keep note of it.
There are indeed other ways to get more cars. If you convert each 2 digit value in the 80 codes to text, you'll get a letter. Each car has it's own code in the game, for example:
[R]Mobil 1 NSX '99s values converted = h2n1r. That's it's car code.
For this example, let's use the Corvette '96. We first need to get it's car code, which is ccrcn. Let's convert that text to hex. It turns into 636372636E.
Now all we have to do now, is to replace the digits for our car. For example...
80028C98 0068 -> 80028C98 0063
80028C99 0032 -> 80028C99 0063
And so on...
Once you've replaced all the 80 codes with the new values, try pressing R2. You should get the Corvette in the Mustang's place now.
You can find most car codes here:
http://www.lecoyote.net/gtweboldbc/gt2actio.htm
Hex to text:
http://www.string-functions.com/hex-string.aspx
Text to hex:
http://www.string-functions.com/string-hex.aspx
Hope that wasn't too complicated.