Extend a class that is already being extended

Ok, I have spent a little time searching and I can’t seem to find an answer to my question, maybe I’m asking the wrong question.

here’s my situation:

I have a document class called Main.as, this class has variables that instantiate a CreateShape.as class that acts as a superclass. The CreateShape.as class has a protected function that is overridden by other classes (I have a CreateCircle, CreateSquare etc). Those CreateCircle etc classes, use extends to extend the CreateShape.as class, and thus have the ability to override the main method (called newShape()).

Here’s my question:

I want to add more functionality to my CreateCircle etc classes. How do I add other classes and their methods to my existing classes that are already extending a superclass?

any help would be appreciated.