[DNSB]

I agree that the only reliable method is an epub editor and the Mark One eyeball. As usual, do all the dirty work on a copy or using Sigil's Checkpoints. The copy is my preferred method.

And then you have the epubs such as Gutenberg where you can have multiple chapters and partial chapters in a single file (the last one I edited, chapters 1 & 2 and the first part of chapter 3 were in a single file with the title page, contents, etc. while the last part of chapter 3, chapter 4 & 5 and the first part of chapter 6 were also a single file.)