[itsme]

You can use "Custom Group" and name it as you like in Library Settings.

Far more flexible is another feature request to add more custom fields and custom groups, see the post above from 2015-12-23.
Mike is very busy and has to prioritize what to implement.

My preferred solution would be a field "Involved Person" combined with "Role"
"Involved Person" should have its own metadata (e.g. day of death is essential for European copyright). "Role" should link "Involved Person" and "Song" and take values like composer, lyricist, arranger, artist, conductor etc. I'd like to be able to freely specify and name both roles and metadata. But that requires lots of changes in the database structure so that I don't have hope that it can be expected.