The charmap format isn't documented because there are both load and save functions, and trying to recognize unknown characters will automatically add a stub to the charmap in memory. Load the charmap (a blank file will work fine), try to recognize some text, then save the charmap. Load it up in a decent text editor, and modify it. Then you can repeat to taste.

This should quite likely be clearer in the POD -- suggestions welcome. I'm not terribly good at forgetting what I know about the module in order to write the documentation for it. (And, alas, I'm not terribly good at follow-through -- I tend to get stuff working well enough for me and then stop working on it. This time I managed to get a little bit further, and do some cleanup, release, and then stop working on it.

PS -- /msging me would have been helpful -- fortunately, brother Limbic~Region noticed this and /msged me.