This would allow you to change the default schemas as well as introduce new ones. Even if you tried to do an overlay of image, application etc it won't work. I do not have an answer on why in this particular instance it's not working for you but have an OOB solution that doesn't require any tinkering.
Thanks you for your concern, if i modify the default schema from the url directly it will affect the whole AEM instance, can't i use the OVERLAY concept for the DAM Asset editors like other components?
Finally found the article that explains this. You can't overlay this option. It has to be added manually or via package deployment if you desire