Tim Buell has a series for Dorico/Drummers. In one of the episodes he describes how to add a circled notehead to signify the open hi-hat technique.
When you want to enter an open hi-hat notehead, you must first enter the closed hi-hat notehead (MIDI #42), then touch Option/Shift/Up-Arrow.
If you enter MIDI note 46, you get the default degree symbol above the slashed stemmed notehead.
How do you edit the symbol assigned to percussion MIDI note 46?