Not much point asking Motability about the AP drop as they will simply state their policy, which is that you pay the AP that applies at the time of order. It is a matter for your dealer as it is really down to their discretion. Sounds as though they might be willing though, so good luck. The AP on my new car order dropped a few days after I ordered and the dealer proactively cancelled and re-ordered without me asking them to (it was only £100 so I didn’t have the nerve to ask, but they said the £100 was better in my pocket than Motabilitys). The process of cancelling and reordering with Motability took just a few minutes and we did it over the phone. Within minutes I had an email confirming the new order and lower AP, so it’s a very simple thing to do and a good dealer shouldn’t object to it as it costs them nothing other than a few minutes time. The actual car order (with the manufacturer) is unaffected.