So, according to
https://manual.calibre-ebook.com/sub_groups.html , my #cgenre category was created (semi-) correctly for my purposes but needs to be edited and better defined.
Is there a way to add a top level field in a mass edit of the column? for example, I currently have something like mystery.cozy and mystery.hardboiled but I need something like fiction.mystery.cozy and fiction.mystery.hardboiled for many books (in this case "Fiction" is the library. But I have around 10+ libraries and >1000 books.