save any file at folder 99 file 20 with a cleared name, or just call it 'clear', and just assign that to each space to erase the previous entry. Use an initial sequencer on its own if you want to clear the sequencer, or maybe an initial current panel on its own if you want full keyboard piano, or a local off or full mixer at zero to mute everything in the event of pressing the assignment by accident when you want no sound output at all.