I have an interesting (to me anyway) idea:
What if we added a default option to the GRC-XML-to-python converter to add the contents of the original GRC file as a big, delineated comment blob. Then, a simple tool could pull the GRC back out of the python file anytime and you could go back and forth. An option when building would disable the verbose output for those publishing code or who just don't want the extra cruft.
It's a little lame, but it solves the problem. I know I've had to hand-craft many old GRCs from python files when the original GRC was lost or the originator was other than myself. The problem has often crept up with GRCs not properly updated for new versions of code, where the blocks go missing in the GRC representation (I think there was talk of fixing this - graying them out or something).