Write ``<a:gd>`` elements to the XML, one for each adjustment value.
        Any existing guide elements are overwritten.

def _rewrite_guides(self):
        """
        Write ``<a:gd>`` elements to the XML, one for each adjustment value.
        Any existing guide elements are overwritten.
        """
        guides = [(adj.name, adj.val) for adj in self._adjustments_]
        self._prstGeom.rewrite_guides(guides)