New Test Version
Contains changes from last post, plus adds a Preferences option for 'Edit Metadata'.
It defaults to off, but I also added confirmation dialogs (with 'show this again' checkboxes) to explain it.
It also means you will 'Edit Metadata' for 'Per Section' books if it's checked.
FYI, I've looked into multi-level TOC -- I don't think that's going to be happening in EpubSplit.
