Thanks @Kezo. Just for the record, I don’t currently have a Motability car. This is my first.
I take it you have your own car at the moment? If it were me in your situation, I would firstly be following BigDave’s advice regardless. I would also ring around different dealerships to see if they have your chosen model in stock they are willing to let you have (the trick is to firstly ask if they have any in stock as you would as a normal retail customer. If they have then ask if they will be willing to let you have it on motability) or ask if they have a dealership order placed they will let you put your name to. Its also worth travelling x distance if this is the case. Your not tied to this dealership!
Are you dead set on having this particular car or are you willing to broaden your search?
Finally take a look in the deals and offers thread on here.
For your own sanity don’t take a car you won’t be 100% happy with, just because the dealer offered one. Motability won’t look kindly if you ask to change it prior to 3yrs especially with it being your first car on the scheme. If you were already in a scheme car I think Motability would have backed you far more than they have done, which is sad really.