I'm not sure how applicable this would be to your situation, but I have an enumerated (fixed set of permitted values) column, #booktype:
I have a virtual library for each of them.
Assuming you haven't already merged (or at least still have the originals to merge from), you can use 'copy to library' on one library at a time (make sure #cgenre also exists in your new library!) and then bulk-edit to add your source-library entry.