I had the same question and AJ told me the same.
You must find the voice you wish to edit - say a trumpet voice - in the voice list. Then hold the icon for that voice for a 2 seconds and the edit screens become available. Then after applying your edits you must save the voice with a new name and it will be available for you to use in whatever styles or registrations you wish. I wanted to save certain voices with the octave changed up or down and that was the answer I got.

Deane