Bogdan is correct, we can't because the keyboard makes you delete what is in the channel if you want to record anything there.
But I have wondered if you use the new "midi to style" program and just record a midi file of say 10 to 20 bars long of just the MAIN (A,B,C or D) that has the CHD1 pattern you are wanting to edit.
Then have the program make a style for you. If you then put that style into the "style creator" and opened it, would you then be able to modify the CHD1 channel?
I still have not found time to work with this new program.
Drake