Changing the shape of a shape note

In the attached piece, I used Staff/Part Properties to change the noteheads from round notes to shape notes, but I am wondering if I can change just the grace notes back to round notes. In the shape-note tradition, grace notes are usually written round. I tried Noteheads in Palettes, by which I see I can change the notes of a piece written in conventional round notes into shape notes one by one, but after I convert an entire piece into shape notes, it doesn't let me change any individual note to anything else.