Get a spare car and let them do it. That is my advice.
Why? Software is useless without hardware. They simply do not know the effects of their software updates on all hardware versions. And my gut feeling is that MG sells cars far too often with different versions or even brands of hardware. And, if a given version IS TESTED to work with the new software yet it does not in on case, they must first exclude hardware faults. So they need the wheel to find out what happens. Then they can possibly fix it.
Unfortunately, this is one of the reason the MG is cheaper than its competitors.