As far as I know, it's not yet possible to edit the names of Bookmarks. Because it's also not possible to tag a group of recipes or books and add a Bookmark to them en masse, the workaround is fairly cumbersome if you want to change a Bookmark with many recipes/books. You have to tag each recipe/book individually with the new Bookmark, then delete the old Bookmark entirely.
Off-topic, but just noticed that the Indexed Books odometer quietly turned past 6000 over the holidays. Dang, missed my chance to get out of the car and run around it once or twice...