Sounds like it might be easier to just write a program which inserts line breaks after periods (and one to remove them), so you can edit the books in their typi

Sounds like it might be easier to just write a program which inserts line breaks after periods (and one to remove them), so you can edit the books in their typical format and export to "git format" to deal with versioning/branching/etc. Although it sounds like you've been doing this for a while so there's probably some reason this wouldn't work which I don't know.