Originally Posted by kiwidude
I've tried that tag approach for this but to be honest I just don't like it for this purpose. ...
Lots of ways to skin the cat, one of the great features of Calibre
Having thought about it a bit, I can see where you are going with the right click and assignment of selected items to user categories. It looks useful, and Kovid's leads should help you on your way. I'd encourage you to submit it as a patch.
To be sure I understand, you would select books, then you would right click, choose "Add to user category" which would expand to list all the created user categories , and you would choose one of the user categories, which would then expand to show these options: "Selected authors" or ... or "Selected series" or Selected Tags"?
Behind the scenes, all the authors in all the selected books would be assigned to the selected user category if you chose "Selected authors"?
Would you assign all the tags on all the selected books if you chose "Selected Tags"?