I used the group editor to make the legs a separate material zone.  Weirdly, it didn't work at first.  I may have screwed up, or it might be that memory issue (where old textures stick around in your cache). 

But I saved the original "skin" texture as a material to the library, and was able to apply it to the legs after the snow was generated.  That worked.

Though after all that, I think I like the original version better.  Might try again, with less snow applied to the legs, rather than none at all.