I'd say replace it with a Seoul because the Seoul has a closer beam pattern when compared to the Luxeon. If you use a Cree, more of the light will go into the spill.
You'll have to isolate the positive slug to prevent shorts(a bit of Arctic Alumina should do, apply a thin layer of Arctic Alumina and wait a bit for it to partially cure, test the resistance with a multimeter then place the Seoul and solder the wires) and a
0.03in raise in height to get the right focus.
I head the Seoul has a slightly bigger bas then the Luxeon so that might be a problem.
I haven't modded yet, just been reading a lot.