If I’m not mistaken, user @thlayli_x has written a Python script that reads tags using an external tag reading library (mutagen) and can insert any tags back into the Plex database. Best to contact him/her for details.
If someone else is having set “prefer local tags” and is struggling with styles showing up: this week @thlayli_x improved his Python script which imports Styles from your local files.
Now my Artists and Albums are displayed with Genre and Style tags like Discogs structure.
I want to take my off to @thlayli_x and say: thank you!