Is there a shortcut for adding parentheses to a courtesy accidental? And can this be set globally as a preference?
Yes. In key commands, search for “toggle accidental” or something like that.
For global (per-flow) settings, see here:
Note that there are four choices in Properties > Notes and Rests > Accidental, so this command cycles through them all. (The word ‘toggle’ is a misnomer.) The first time does Show, then Hide, so to get to Round Brackets you’ll have to hit it 3 times.
For your purposes, check out Notation Options > Accidentals > Cautionary Accidentals.