Overriding Non-AS3 Namespace Accessor Methods Using Class Prototypes

If you do not use the AS3 namespace, an instance of a core class inherits the properties and methods defined on the core class’s prototype object.
Is it possible to redefine the accessor methods for a property of a core class instance by using the prototype object of that class while using the ECMAScript/non-AS3 namespace? For example, could DisplayObject#mouseX be redefined this way?

I would guess that it isn’t possible, as there isn’t really an analogous prototype-based syntax for the accessor method definition syntax. It would be pretty neat if this could be redefined, though, which is why I am asking. :bounce:

Also, how are accessor methods (internally) defined for core classes when not using the AS3 namespace?