HI,
A long time ago, i started to write a tag editor , some notes can be found here : https://dl.dropbox.com/u/74887749/kpa_tag_inspector.html
it was simply providing a way to edit tags from rig files, waiting for a more complete product from the mothership, but as I got almost no feedback about building a platform independent installation package, i stopped its development.
Like Armin said, it's a lot of work
More information can be found in an old thread called "Basic Rig Tags Extractor/Editor" in the "Introduce Yourself" part of the public forum.
Laurent