I need this function too.
In my OWN dictionary, performer includes every people and group who are making sound.
Simply, performers are superset of {singers, instrumental players, choirs, ensembles, conductor}.
I'm using ARTIST field to represent singers and instrumental players, CHOIR, ENSEMBLE, and CONDUCTOR for others.
Like above, classification of artists may be differ from one people to another.
It would be useful if I can customize the role drop down list (in addition, if I can use custom tags)
Thanks.