The MiniStar2 is pretty much a drop-in affair. The only other article you'll have to swap out is the reflector, but that's an easy and tool-free process too.
From my website, here are the complete installation instructions:
To change the bulb in the Mini Mag with the MiniStar2, unscrew and remove the head, remove the old bulb, and insert the MiniStar2. If it doesn't light up, remove it, give it half a turn, and reinsert it.
Unscrew and remove the retaining ring on the head, and remove the reflector. Replace it with the one provided with your MiniStar2, and screw the retaining ring back on. Now, screw the head back onto the flashlight body. The MiniStar2 should go out when the head is screwed all the way on, just like the original bulb did.
See? Easy, isn't it?