Re: Rear light cluster removal –
If they are the same fitting as Mrs F's old A3, then each light unit has a small sperical 'nodule' attached to the back of it, up towards the leading edge of the light. This fitment engages into a corresponding hole in the car body, and is quite a tight fit. Once the nut holding the light unit has been removed, it's just a case of wiggling the light backwards and outwards gently, until the fitting pops free, or as ruggedscot suggests, you can try gently levering with something that will not mark the paintwork.
2016 A6 Saloon BE Ultra S tronic - Floret Silver, Tech Pack Advanced, Parking Pack Advanced, Heated F+R Seats & Wheel, Electric Seats, Matrix LED, Ambient Lighting, Speed Limit Display, Twin Spoke 20", Folding Memory Mirrors.