To get at the lid, you pretty much have to disassemble the whole unit. You have to remove the keyboard and palm rest. Disconnect the cables from the display (4-5) and then unscrew the hinges. With the display separated, you have to pry apart the display bezel.
At this point you can get at the webcam without anything else, but to replace the lid means removing the actual display from the lid, then put everything back together. It is not difficult (unless you don't follow instructions well or are impatient), but it is not a 5-minute task either. I just had my Mini apart down to the display bezel removed to fix a problem I had caused with routing the display wires. Took me about half an hour and that was because I had done it before.
If you are simply swapping the whole lid (with everything in it), that's somewhat easier - at least you don't have to pry apart the display bezel. But you do have to do most everything else.