The L1P/L2P is one of the easiest lights to mod. I've done a few of these already... in fact, I've just put a high CRI Seoul in one (it rox, btw). Never had any problems getting the pill out. A pair of needlenose pliers, a strap wrench and some heat always get the job done. If you think this is hard, try taking a KL4 apart, hehe.
A P4 works really well with the L1P/L2P reflector and throws a surprisingly nice and smooth beam. You might want to sand the back of the relector though to shorten it approximately .03" for best focus with the Seoul. If you don't, it's still going to work fine, but the output will be a bit more floody.
Oh and as always, make sure to insulate the positive base of the P4 properly...