I found
https://github.com/ErikLevin/calibre_rpggeek_plugin
But it gives very unclear directions on how to compile, for those of us who don't do such things... so I'm lost after getting terminal to instal it...
I now have errors when I do test, not sure how to proceed -- but since you were trying to do this, maybe we can find a solution...
------- calibre_rpggeek_plugin % calibre-customize -b .
calibre-debug -e test.py
zsh: command not found: calibre-customize
zsh: command not found: calibre-debug