↑ ↑ ↑ ✔️
Several years ago I tried, and failed, to edit the Kracked Press en GB hunspell dictionary. I also tried and failed to create a domain specific dictionary. I was surprised there were no tools specific to the task - no demand I guess.
Today, I could possibly create an epub from scratch with notepad and pkzip - but only because of what I've learnt from using Sigil
On reflection that's a big 'possibly', if they were all I had.
BR