91 series rear sight

[Salt Flat]

Just from looking at some pictures, I think it's like a rivet in which case you would have to grind the head off With a Dremel. A new rivet would probably have to be made or the old one have some material added to the end (weld). Then rivet it back together. The wood part looks like they just upset the ring around it in an inward direction. You could pry the button out but it will probably break. A new one could be sized closely and epoxied in. I don't have one of these in hand so this is just a guesstimate.