Just edit one, right click on it and select "Apply Sort Field" -> "All Matching Fields", and the entry will be copied to every other entry with the same artist name. For example, rather than group edit all entries of "Paul McCartney" to "McCartney, Paul", you only edit one song, then select "All Matching Fields", and the sort name ("McCartney, Paul") will be applied to all other songs with the artist "Paul McCartney" in them.