The AP on the car I ordered dropped from $1499 to £749. The dealer left the factory order in place and cancelled the old MB agreement and resubmitted a new MB agreement. It only took him a few minutes to do that, or would have done if I didn’t need quite so many driving adaptions. Adding the adaptions takes the time because the MB adaptions ordering process is a bit of a faff for the dealer, I was with the guy when he re-submitted the order.
£750 is a lot of money to lose. Although one of the adaptions had gone up by £50 so I saved £700 in the end. It helped towards the cost of having the adaptions fitted.