Bob, piece of cake. I am doing a DD 18650 TYOJ IMS 20mm dual-level mod RIGHT NOW on the TT 2L.
Unscrew the bezel.
Leave only one 123 inside and shake it a few times, the light module will just push out the bezel end. It was that easy. You might need to use something to push it out if the shake trick does not work.
Also, if you want to separate the head from the battery tube - boil it and use strap wrenches - done.
My mod looks easy except boring the body might be a little harder than the rest. Anyway, I could use a 17670 if I had too.