that could be said for all option extras a dealer had to offer,, heated seats , leather seats, towbar, basicly any extra its you the customer thats paying for factory fitted extras. some extras are cosmetic but some make driving better or more comfortable for the customer.
If you were to ask for a window tinning company to do it after you get it , then maybe.
i do not think motability see the added extras on the the application form the added extras are on the dealer order form.
phone another dealer add ask about the windows see what they say,
you could cancel that order then go elsewhere place the order with tints .