I'd gotten the idea that ZLs were press-fit and epoxy throughout. Very difficult to disassemble.
STP, I'm sure you know that drill presses aren't designed for side loads, so milling with them isn't good for the machine. Depending, you can add runout to your press that way pretty easily. I own an actual mill, and I'd still not try it, because the bezel is stainless steel, and I haven't the high-end cutters for it. You'd very likely sacrifice both the ring and the lens, and probably have to face off the aluminum, too. Doable? Yes, by a talented machinist. Worth it? Not for one. UNLESS: You made this a cottage industry, and were able to offer a "threaded bezel" package for ZLs, and were willing to find people who'd pay more than the light costs for the upgrade.
I've thought about a threaded bezel too, and I think the easiest way to get that is to epoxy on a female threaded ring, that would sit to the outside of the existing SS bezel. That would still leave you with the challenge of making your own filters. At this point the Sparks become very attractive, since they come with threaded bezels already.