Yes, they can adjust the AP at any time prior to delivery, as long as the car remains on the scheme.
If the car is removed from the scheme then the order can still be honoured, but at whatever AP is assigned to the order on the Motability system at the time.
Either way, it’s in your friends interest to get the AP adjusted ASAP and if the dealer plays silly buggers and won’t do it consider cancelling and re-ordering at another dealership.