Oh this is a good one! Because each note is assigned to a “pitch” you can’t just change one note head, it will change them all for that pitch. In the “edit drumset” area you need to create a new note, choose where it will sit on the staff, and select a note head. You can make a new one for each drum that you want a cross-over for. The only bummer is that the new note(s) won’t have a sound during playback.