Actually I agree with you about the Carrera GT. If there was that car in the game plus a realistic echo in the tunnels I would never be out of it. But thats just me dreaming.
I have no idea if it can be done but who knows what the future holds? You may be able to soon as the modding community for this game is in early stages. I guess it will probably be possible but not sure so theres not really an answer to your question.
I do hope some of these cars come to TDU at some point, be it from Pro Street or whatever. If I wanted some cars from Pro Street they would be the Veyron, CCX, Carrera GT and the Zonda F. Those were cars that TDU should have had or are missing from the game ;)
The words "Pro Street" are not a good thing to really mention here. The reason being is that people think you are on about bodykits and parts and what not as it was what you said in your first post and that got me thinking about ricers etc.. You should have said about the original cars and supercars that TDU should have had and that Pro Street had. It would have got a more relative set of replies.