There is no implemented option to customize these markers.
The content of the infoWindow may be modified by using a custom infoWindow(via the infoWindow
-option of the DirectionsRenderer ), listen to the domready
-event of the InfoWindow and modify the content
....but this InfoWindow will also be used by the origin/destination-markers, there is no way to differentiate these markers from waypoint-markers.
The best you can do is to use the suppressMarkers
-option to hide the automatically generated markers, and create the markers on your own based on the DirectionsResult
.