Some feedback.
The engine size doesn't work as it should I think. It doesn't actually change the engine size for what you ask. And In the XRG for example, you can only have sizes between 1000-1500cc.
Cylinder amount would also be good to have. And all the tire parameters, and well, all the stuff what was in the old tweaks actually. :P
The program actually seems to works on all cars, but it uses either the default or your previous values which make the cars ridiculous anyway, but it does. I managed to get it confused while trying what cars it could do, and it didn't recognize I changed back to a car it supported.