Im new to programming myself, having focused mainly on 3d modeling and level design. I do believe the term is called function overriding or overloading. You create a custom class that either is a subclass of the engine class you want to edit andor you import that class into your class with the #include directive. Once you do that your class will have all of the functionality of that class including any new functions you write in your class. If you want to change a function that exists in the original class that you extended from, you need to re-write it with custom parameters. Heres a link to a wiki page : Function overloading - Wikipedia
Someone help me out here.