Just to update everyone we eventually got this sorted! After a week of back and forth, Motability were able to update to the new VTN code for the facelift model and kept the advance payment at Nil. It took as much as Motability putting us on hold while they got the dealer on the other end of the line to sort it all out but after 45 minutes it was all done and we picked the car up on Saturday.
Well done. There should never have been any other outcome, as the AP you pay is always the one that was applicable at the time that you ordered. If a facelift happens between order and delivery then that’s your gain and dealers have no right to attempt to re-negotiate. The Motability small print is more likely to apply if an all new model comes out with different trim levels, specifications and prices, but that wasn’t the case in this instance. I guess this is going to happen a lot with many lead times now extending to a year or more. In this case, however, it was nothing more than a rogue dealer chancing their arm. At least you now have the measure of them.