I've only read that body kits wll be available for some cars, PD did'nt specify wether they were race mods, you could presume they are which they probably are but PD's wording could mean a couple of things.
And James1985's idea about the sponsorship, I like that idea it would make you drive all your cars so you get sponsor for all of them as well as giving the car decals and getting sponsorship money, it is possible but I doubt it will be in GT4, PD don't have the time to implement anything like this, GT5 maybe.