we can change the icon of markers, i did it on right click event. Lets see if it works for you...
// Create a Marker
var marker = new google.maps.Marker({
position: location,
map: map,
title:'Sample Tool Tip'
});
// Set Icon on any event
google.maps.event.addListener(marker, "rightclick", function() {
marker.setIcon('blank.png'); // set image path here...
});