There’s no reason they can’t, it doesn’t affect the factory order or how much they make from the sale, it’s only the amount you pay Motability that changes.
All they do is log in to the Motability system, remove the order and re-submit it, takes less than 5 minutes and as I said is at no cost to them whatsoever.
Personally I’d ask for the sales manager or a director, if they refuse cancel and re-order a Sportline Plus elsewhere and save £500 on your original order, should be about 4-6 months at present I believe and at that time you may get the improved 85 variant when it turns up in the UK.
Please excuse spelling/typos. Apart from being a clot it turns out I had one on my cerebellum that's now causing various problems!