If you use an oversized drill bit you can 'gently' take just the 'cap' off the rivet. That will leave the body of the rivet still attached. After repairing, or in my case, re-glueing the leather back in place, you can use a button head self tapping screw (8g x 15mm) to re-attach the armrest. Screws are known as timber stitching screws here in Australia.