That's very useful information, I have the plug for that MID socket (mine is white) but didn't have a MID unit because the original NAV unit is same dimensions as my aftermarket one.
there are some similar X5's near me maybe its time to don my nice voice and knock on a few doors, as you say its only needed for a few minutes.
My head unit is identical to original but has SD slots for input source and nav updates.
I have every connector still attached behind the unit (no damage at all)

concerned that the MID units I see on Ebay uk list for radio display when my NAV unit included radio display.

Do we know if its the BC button on a MID that allows CODE entry?

BTW thank you for all the comments/advice so far - great forum