The only problem i can see is switching a two door for a four door visa versa but since your not ment to do that its really use at your own risk, i think custom cars are the way to go, mods maybe not though most custom cars use the dmagic wheels thingy, which is a modification, custom cars wouldnt have to be switchable if the default handling was embedded or encoded to a file or the main excutable, then if the handling WAS modified the handling embedded could be exticuted tempilry overwriting the edited one