I can'r ignore your request as I have said on a number of occasions in the Forum, that we should all be attempting to edit something in this game to keep it fresh and alive. Good on ya for making this committment.
DL the DTR2 Toolbox or the De2 Editor to get you started and you will find either in VLR's DL section under Editors. Next it's understanding the poly's/vorteces to move as to create ur masterpiece. You have 3 views in editor top/side/front. The object is made up of dots which translate to Triangles. It's understanding up and down and in and out (East/West) in order to move this triangular panel to where you need the new shape to be at. Bear in mind that it may and no doubt will move the next panel above or below or beside. R U with me so far?
There are Tutorials out there to explain the Editor, better than I have. Remember there are 3 car bodies for the game within the one De2 file called a car. Each of these also need to be changed which is a real pain.
Ur other option is to get FY1 or Shock or Jammin to teach you the basics of Editing in Rhino which is by far the best approach and U learn on the one Editor instead of doing things like I have the hard way.
Good luck.