Yes, it's possible that way, of course. And certainly more practical if you have many rules (say, 50 or more). But I also found there is an option to export and import the rules (I didn't notice it before for some reason). So I did that (naturally I checked the existence of conflicting rules before the operation). I had only about 10 rules I wanted to transfer, so the export-import option was faster than creating a new library.
Calibre rocks!
