Firstly, thanks for the brilliant in depth-guide - really well put together and really useful
I've updated my serif font, and deleted and re-added all of my books, as you say to in the guide. I'm using a UK 505, by the way, and I only use Calibre to manage my books.
However, only some of my books use the font (a really small minority) - most are still using some kind of Times Roman-esque font. I should also mention that Most of my books are epubs - none with DRM, and a fair few from Feedbooks. Is this a case of embedded fonts? It's a pity, as I'd love to read them with a nicer font. Is the only option here to edit them by hand, or have I missed something? Is it possible to add a CSS rule to Calibre and get it to re-convert them into a new epub?
Any help would be greatly appreciated!