1-Pull small -B spring out.
2-Firmly grasp aluminum "slug" with needle nose pliers and give it a firm TUG. Watch out for the little nail/rivet thing, keep that for re-assembly later.
3-Clamp a dime or penny in vise-grip pliers and use this as a tool to unscrew the black plastic retainer. Mine just unscrewed with a little force. I didn't need to heat mine, although other CPFers have reported needing heat treatment.
I have done this 2-3 times on each of my Z41 tailcaps. So its somewhat reversible. Although I imagine theres a limit to the numbers of times it can be repeated on the same switch. I had my M2 switch set up as a rev-clicky, and didn't like that at all so I switched it back to the OEM Z41. I upgraded my 6P tailcap with the Moddoo low resistance guts.