I'm not familiar with these lights so bare with me, but what's going on with that pink piece the bulb is fixed too? The part that has what looks like NPT threads.

It almost looks like a pill:

SKU 1208606

Yah, a drop-in is the pill, emitter and reflector and contact spring. It's just the assembled parts. Since you don't need the spring it's probably easier to build it from parts. I'm honestly not seeing a lot of DIY parts on FT though. I think the maximum for an XML is 3A and the functions have no effect on max output. Lumen, lux, watts/m^2, I find those numbers meaningless. You can basically only put 3A to a single die XML and you get what you get :D

The reflector in a reflector looks like an easy mod. You just have to cut it further down where the fat copper part meets the skinny 18mm copper part. You have to be accurate with the cut though, there isn't much of a lip where the reflector screws onto the pill. Worst case scenario you might have to put a little epoxy on the back side (you're basically screwing the reflector from one side, the pill from the back and pinching the existing reflector, you can see fro the pill pic it isn't much)

A battery holder like one of these would probably work:

SKU 4328000
SKU 9656661

but you could get away with one of these if you wanted:

SKU 1279500

Hope these ideas help.