If you change the tags within Plex, it will only be stored in Plex’s database. You could have to re-do the changes if the database is damaged, or if, for any reason, you remove the album from Plex and add it back again. There is no ‘lock’ icon on the Album Artist field in the Edit Track dialog, like you see on ‘Title’ or ‘Artist,’ so it probably won’t be protected if metadata is refreshed.
Editing the tags embedded in your music files is, in my opinion, the most secure way. If you are confident in the completeness and accuracy of your embedded tags, you might want to be sure Plex is fully configured to prefer embedded tags.
You might want to check out this guide if you go that route.
