One of my custom tags is "subgenre" for my classical collection. I'd like to have things like "Piano - Solo" or "Concerto - Flute", but I don't want to have to memorize the exact formatting of every new subgenre I create. Is there any way to define preset values (that would appear as a drop-down list) for custom tag fields within MP3Tag? For example, the "Genre" tag has drop-down choices such as Punk or Ambient.
That's not possible.
But you can create a format value action for each subgenre that you use and quickly apply it from the down arrow besides the button.
If you use a # sign in the action group names it will give you an extra sub menu:
Tag Subgenre#Piano - Solo
Tag Subgenre#Concerto - Flute
button.