Feature Request: Batch Add Tags without Removing first

Use case: I have my tracks organized into a bunch of playlists with my own genre subcategories. There is often overlap in tracks between these playlists, for instance, "House -> Funky", "TechHouse -> Funky", and "House -> Jackin" may share many tracks.

I want to add these categories as tags as well, like "House, House/Funky, TechHouse, TechHouse/Funky, House/Jackin". When I have a playlist where some of the tags overlap and some do not, I do not want to remove existing tags in order to add new ones; the existing tags are important and should remain. I can't re-add them easily since there may be different tags for each track in a playlist.

This isn't super important to my general workflow right now since Tags don't have much purpose besides in MIXO yet, but I'm looking forward to the day when MIXO allows Smart Playlists, and/or supports exporting Tags to other software so I can use the tags for Smart Playlists in Serato or Rekordbox.