A pair of sir-clip pliers springs the collar off, quick file to the sides of the rivet head to take the splay off and punch it through. One end of the rivet generally only has a slight splay so dosn't take much, can re-use the rivet on re-assemble and just round over wit ball-pin hammer.
I plan to do some step by step pictures next time and will post them up.
Looking at the hole that the pin that holds the blade and the socket for the handle it looks off centre so it might be an idea to drill that before you round the end off, then round the end to suit the hole? Just a thought.