Never heard of such a thing but I can’t see a dealer turning away extra money, so it may be the case. I would give Motability a call. If it’s new policy, it’s going to affect lots of people…
….and, of course, it would affect Motability even more, as we pay in full for the optional extras (including the VAT that Motability doesn’t pay) and yet come end of lease resale, any additional value achieved as a result of the extras is all extra profit for Motability!