Edits to stem direction in drum set don't affect existing notes unless they are explicitly reset

I believe you'd need to change the voice that note is assigned to. Voice 1 and 3 for stem up, 2 and 4 for stem down

Hmm, actually both should work and does for me, so I can't reproduce the issue

I think it's a known fact that edits to drumset definition don't apply immediately to existing notes - only to notes not yet already entered. If you wish to reset notes already entered to the new default, just select them and press Ctrl+R. Not sure if that's truly by design or not or just a quirk of how it currently works. Worth discussing on the forum.