I've heard that it's possible to modify a non tri-sound Super 80 to make it tri-sound.
Does anyone know how this is done?

Any standard humbucker will have 2 coils that are connected together(assuming 2 wire). Some pickups(V7 & V8 for instance) have a wire attached to that same point and brought out for coil tapping. stewmac.com sells 4 wire pickup wire and you would unwrap the tape around the 2 coils, unsolder the old wire and solder in the 4 wires so you get each coil separately. Check out the wiring diagrams available on the web and pick a color code. I did this mod on some DiMarzio PAF pickups back in the 70's and it worked fine(as long as you are careful not to break the tiny wires on the coils).