Driver is held in place by retaining ring that is easy to unscrew. Front of the head unscrews easily, which gives you easy access to the emitter.
Today, I took the the XM-L2 T4 6A3 out of my ZY-T29. That emitter founds its way into my Roche F8, which runs a DrJones lucidrv.
My ZY-T29 is now ready for 3,5A. Should be looking at 1100+ emitter lumens later this week. :)
The DrJones Lumodrv driver circuit is what really transforms the light. The stock 2,8A is quite nice for the light. Especially considering that you can program high to be lower if you want. Or you can easily ramp down the output a little. This thread shows how they can be put into a light. Oh, btw, my K2 is now pushing 4,2A (with the right battery).. More updates to come in that thread later..