Hey guys - I have a Yukon HL and I popped mine open a few days ago. I've removed the LED housing and removed the old Lux LED. I've also identified the wiring and found that, jeez, this light is regulated to a T. The voltage and current output are astoundingly flat.
I'm planning on dropping in a Seoul SSC P4 in the Lux's stead. I should get those on Friday.
If you guys want some pictures I'll feel free to post what I've got.
The LED emitter is pretty interesting - it's housing on a raised heatsink, and there is a second heatsink screwed down on-top of the emitter, aiding it's heat capacity and compressing the LED against the first. The emitter is pancaked to to the heatsink with thermal paste. Just pull out the emitter housing (will have to break the positive wire leading to the housing), unscrew the top heatsink, and voila, you have your older Lux replaced out with a Seoul.
Emitter swap worked well for this guy:
https://www.candlepowerforums.com/threads/151400
Same basic principle, same reflector type - should do well with the Yukon HL.