Custom memory is a separate section of the keyboard's memory. Don't worry about losing the original built in styles, etc. The factory settings including all the sounds, styles, etc are safely stored away inside the keyboard. See Page 176 of your manual to see how to restore most factory settings with the INITIALIZE function. You can always get the keyboard back to exactly how it was manufacured that way. I have never owned a KN6000 but think a disk was provided that contains factory custom memory files. Maybe someone else on the forum has that data.