First of all Buddy to the best of my knowledge when you add rhythms into the custom memory they delete the ones already in there, so that wouldn't work would it...
If I were you I would transfer the existing 10 rhythms from custom memory to Memory A one at a time and save each one to a floppy disk as a seperate saved rhythm.
Then load the new custom memory rhythms to the custom area on the keyboard which I seem to remember happens automatically when you click load from the floppy disk that they are on.
You may then if you wish also transfer them one at a time to memory A also and save them to a floppy disk one after the other.
aah it's so much easier with a KN7000...chuckle.
Failing which I'll have to come up to London and show you how...
Rog