Add breath mark to all staffs in score

Sort of. If they all have a note of the same duration n the same beat and you want add the breath after it, just select that vertical slice (eg, click one note, Shift+Down to extend), then double-click the breath mark. But this won't work so well if the last note before the breath starts on different beats and thus has different durations across staves; you'll end up with too much selected.

I guess it might be nice to have a "add breath before selected note" command, because it's much more likely those will align across staves.