When you select a record and Load it to play, press EXIT to go back to main menu.
Make what changes you want to voices, tempo, volume settings, and then click on the Registration on the top of the screen, and save it.
The next time you call up that song in your playlist, it will load the changes you made.
A playlist record is just a pointer to a registration.
So, if you make a change to a registration, it automatically plays those changes in the playlist.
Gerard