The parts are not toggled between on and off, but between default and non-default—so that they once again become transparent to the value of their prototype.

Your $DisplayExpression stamps are listed in the same order as the SmartExpression segments.

⬍ Show Num 
⬍ Show Proticon 
⬍ Show Date 
⬍ Show Count 
⬍ Show Bips

Just select the notes you want to affect and run the appropriate stamp. To affect all notes of a particular prototype, run the stamp on that prototype. To affect all notes period, run the stamp on normal_note.

To restore any modified notes to their default display expression, select them and run the stamp.

For the full list of SmartExpression Togglers, see here.