Dealers add options beyond what's on the window sticker all the time. Most of the time those include a wheel and tire upgrade for about $2K. If they can legally pull those rip offs, I don't see why they wouldn't be able to swap the tires out. They could just put the all seasons on the other car and add a dealer add-on sticker for the option. The only legal problem I see is that they would technically be putting used (even if they only have a few miles) tires on a car they are selling as brand new.