[DaltonST]

I don't need luck. I have 3 plugins in production that do exactly the same thing. I use custom sqlite objects (tables and views) that Calibre knows nothing about. In fact, my Derive Genres plugin uses its own derivegenres.db sqlite database for most of its work. The job connects to that db (not Calibre), and later attaches to metadata.db, reads the data it needs, and immediately detaches from metadata.db. It treats metadata.db as "read-only". Later, it does send a dict back to its callback in ui.py for a "normal" gui-style update of the genres that were derived using the standard set_user_metadata function.

So, it appears that a restart is still, and will always continue to be, required. C'est la vie.