No need to take the mirror itself off. What I did was move the mirror so I could slide a flat blade screwdriver in and prise the clip nearest to the window slightly down, shine a torch into the gap so you can see the clip, its the same colour as the cap. You then need to squeeze the bottom edge of the mirror cover and the black trim under it really hard until you hear it click. The cover will then look like its slightly off at the top its then just brute force to pull it back and up. Goes with an almighty crack and will scare the s**t out of you and will probably fly off onto the floor so put a cover down just in case. When you are replacing it slide it in so it is level and in line at the bottom, hook the inner clip in and push hard and it will click into place.
I'd been putting this off for ages cause I thought it would be really hard but once I knew about the screw driver bit it was a lot easier. Thy're all done now and hopefully never have to touch them again.
Looks like you guys had a great day and good weather as well. Some very arty photos there. Like those plaques that you got the guys Lenny. Hopefully nexy year you'll get a few more attending so could be the start of something big.