> as i understand it, the typical clojure / riemann convention is to use dashes over underscores.

I just checked this with the riemann devs, and it's definetely not a riemann convention. Suggestions are to use whitespace "because it looks nicer" or dots "to play well with graphite".

It possibly is a convention in the clojure world, but whatever...

It confirms my feeling that you shouldn't bother with this renaming and let users use a mutate filter if they want fancy naming.