i did exactly that in march i changed from a 3dr mini cooper to a mini countryman cooper s both auto as my back has gotten too bad to get in and out of the 3dr mini i was 2 and a half years in.
good news was that they have changed the rules ref gcb you now get a prorata payment i got £400.
all it took was a phone call they were very understanding and agreed straight away. asked at the end of jan and i picked up the new car 9th march fortunately just before it all shut down.