Jason, the cork can be cut easily with a box-cutter or even better, a scalpel. (The scalpel's narrow blade makes it easier to follow the curve.) If you do it that way, mark around the outside with a pen to show the exact amount you want to cut off, so it will end up round and concentric with the inside circle. I'd probably try to save work by just trimming it with the disk sander, but that's me - the disk sander probably gets more work than everything else in the workshop put together. Note, this is a 14", pedestal-mounted sander - don't try to do it with a hand tool.
I do not think cutting the lining into quadrants is a good idea. The lining is likely to come apart due to erosion of the clutch face, originating at each of the radial cuts. This is mainly because it is a soft lining - hard linings from car clutches can stand radial cut lines, but I don't believe cork can. At best, it would put a lot of strain on your glue at the leading edges of each segment,.
