Quote:
Originally Posted by geek1011
I tend to create and edit my books manually using a code editor (my favourite is VSCode). I've been working intermittently on my tool, epubtool, which automates some of the common tasks I perform (unpacking/packing epubs, modifying metadata, and performing transformations on the HTML). I used to use a bunch of custom scripts, but I'm currently adding those features to epubtool as I have time.
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... far be it from me to tell you how to spend your leisure hours

but are you aware that calibre already contains loads of utilities for robust, reliable manipulation of the various innards (opf, html, css, ncx/nav, unpack/pack etc) of an epub? Many things can be done in just a few lines of python code. If they don't currently do everything you may want to do you can mix'n'match existing functions to achieve what you want.
Even if you don't want to be bothered writing full-blown calibre GUI plugins you can still access all the same functions from simple python scripts outside calibre. Neither do the epubs need to be in a calibre library structure.