How to add a new note to every chord of a score

I am trying to write a plugin for MuseScore 3.x that harmonizes a melody; it should read a score with a single-voice melody and then add 2 more notes to each note (thus creating a chord), based on some rules. I can not find a way to iterate over the score and add a new note along an existing one. The cursor method addNote seems to overwrite the element and I can not find any API functionality to add a note to an existing element, in order to create a chord (not a chord element - every note seems to be a chord element -, just to stack three notes to create a chord). Furthermore, overwriting an element with addNote seems to break MuseScore. Sample code:

var cursor = curScore.newCursor();
cursor.track    = 0;
cursor.voice    = 0;
cursor.staffIdx = 0;
cursor.rewind(0);

while (cursor.segment) {
      if (cursor.element && cursor.element.type === Element.CHORD) {
            cursor.setDuration(cursor.element.numerator, cursor.element.denominator);
            cursor.addNote(60);
      }
      cursor.next();
}

The above code breaks MuseScore. What am I missing here? Can anyone post a code snippet where they add one more note whenever they find a CHORD element?