This question has been addressed in previous posts, but I haven't seen a clear answer on whether the feature exists, or is in development, or is unavailable.
The question is whether it's possible to create user-defined lists of artists, composers, etc. in the same way that a user-defined list of genres can be set up (Tools/Options/Tag Panel/Genres). This would let me select an artist, composer, etc. from a drop-down list of predefined entries and thus maintain data integrity within my collection, instead of having to continually comb through the collection to find & correct errors (e.g. "Anita ODay" vs. Anita O'Day").