Metal miniatures make conversions quite a good deal more difficult to successfully execute and more risky. The metal is tough to cut through and because of the extra amount of force one inevitably applies, the risk of injury is greater. They aren't impossible though and the Infinity range has a good deal of multipart models, which make the process easier, though still not as easy as converting plastic models.
Here is a conversion that I have worked on. It basically consists of a weapon and head swap to create a new unit - the Raiden with spitfire. Sure, there is a new model out representing this guy, but I like my conversion better because it's mine.
The head was clipped off, carefully, and I added a head from an old Nomad Tomcat. You'll notice I really don't care about sticking within one faction, all I want to do is create an interesting model when it is finished. He'll probably get painted over the weekend and I think that will make the conversion work better.
My next conversion will likely be a second version of the Raiden, using a ninja head on the C.Guard torso with spitfire, with Haramaki legs. More to come.