The original PTF file is in the dat file and will not be over written. If you add a PTF file all that happens is that the game see the new ptf file and reads the info from it. This includes mip files, 3do ect. ect.
If you want to race the normal track though you need to remove them. The alternitive is that you can create a whole new track like I did.
if anyone by chance happens to see one of velly's tracks being raced online (especially tona or dega with a big hill in it) please tell me and I'll download it right away and race it online too.