Open NAT3 and open tyour nebtemprepository/programs folder.
Grab the selection of n2p files that you want to change and drag and drop to NAT main window. A table opens up where you can edit names and category structure. You can cut and paste between cells of the table to speed things up. Hit overwrite and you're done. Hit Restart to move on to another batch.
Bear in mind that if you receive any updates to the library that ovrwrites the n2p files, you would lose your changes and need to redo it.