Michael,
First of all, why do you want to change it. Is it not bright enough? Do you not like the beam pattern? Do you not like the color of the light?
If it is all of the above, you can go with a high dome luxeon. You'll need one on a star. To stay cost effective, I'd go with one of the Q3J's that are readily available these days. I think Hotbeam is still selling them in B/S/T. I currently have three KL1's. One with a Q3J, one with an R2K and one with an R2H. Of the 3, the R2H is the least bright with the R2K being the most bright and the Q3J being the most white. The differences in brightness are only noticeable when comparing the lights side by side.
If you want your light to retain its all around usefulness, I'd stick with the NX-05 optic that's in there already. It provides for a good throw with a high dome and still has a good amount of sidespill. If you want throw, go with the low profile fraen. It's all throw with no sidespill. It doesn't have a needle beam, but it just isn't a good up close optic. You will however get the most brightness out of a fraen. They just seem to be more efficient than the NX-05. If you want to use your KL1 as an up close light only, you could go with a McFlood reflector. Almost no throw, but will put up a wall of light at close distances.
You can do a search for KL1 and HD to find alot of info on modding KL1's with beam shots and how to's.
