Hey dudu,
How hard was that mod to do? I"m thinking of modding my L2D with these as well. Problem is, it's not like my $17 Trustfire where if I ruin it I'm not out $60.
I'd say for me (I have very basic soldering skill and only few tools available), the most difficult part is to open the head "without" damaging it (which depends on which and how much glue fenix used), most annoying part "may" be cleaning the old epoxy (again, depends if much of it was used), soldering the led can be a bit tricky when the wires are too short.
Check out this thread, it will give you a good instruction of how to open the head
http://www.candlepowerforums.com/vb/showthread.php?t=168844
If you still can't open the head using info from that thread, I can suggest some other ways I tried. I have so far opened the heads of 1x L2T V2.0, 2x L2d ce, 4x P3D ce (inc. Q5); from my experience, the difficulties vary a lot. I opened the l2t v2.0 and 1x p3d with bare hands, the others some need mousepad, some needs mousepad with pliers, some need even better method. I learned new methods to open them the hard way, only after I scratched them lol (3 are unharmed, 1 has a tiny scratch, 3 with moderate scratch).
But remember, you'll void fenix's lifetime warranty once you opened it. I decided to do it because the probability of fenix's driver dies is very low and in the worst case, I can replace it with some cheaper drivers from DX or KD.
Let me know if you need some more info on modding fenix :]
Will check back again tomorrow, it's almost 3am here XD
EDIT: Another reason why I mod my fenix is because I want to get rid of the gap between the reflector and the LED; some people like it that way because the hotspot is softened out but I think it defocuses the beam and some lumens were also lost there.
BTW, most of my modded fenix were bought when they were on sale

(currently they also are) so l2d costs ~40usd per piece. For this price, you can actually get the new eagletac P100A2 but I find the high efficiencies on multiple modes of fenix lights suit me better after mod.