Further to my earlier post, I further downloaded a program called SQLite Expert (
http://www.sqliteexpert.com/download.html), as I'd rather have a GUI when I'm playing with stuff I don't fully understand. I then searched on "download koboreader.sqlite" and helpfully found this MR posting from Sameer:
https://www.mobileread.com/forums/sho...7&postcount=12. From there I downloaded the KoboReader database, and used SQLite Expert to look for what I need to change. Assuming that the database design hasn't changed all that much since the end of 2010, it all looks very simple - but then things do just before they go horribly wrong!