I recently took apart my X5 with similar thoughts in mind, especially
since one of the existing LEDs is dead somehow. While the freezing
technique worked fine to remove the head, it also removed the rubber
tailcap cover in a way I don't think is repairable (to original levels
of water-tightness.) In addition, the head seems to be a single solid
unit, with LEDs, circuit board, and metal all firmly glued together, and
it doesn't look to me like it's going to be possible to replace the LEDs
in the existing head. On the other hand, it seems like a replacement
head would not be too hard to machine...
BillW