If you can understand Parse::RecDescent then your best bet is probably to try to subclass it before modifying it. If that doesn't work, then try hacking on it.

If this is a concern, then why don't you send a line to the author who supposedly is actually at work on Parse::FastDescent. Perhaps you can get utf-8 as an option in the new module.

Cheers,
Erik

Light a man a fire, he's warm for a day. Catch a man on fire, and he's warm for the rest of his life. - Terry Pratchet