How can we create different functionality to objects of a same class?

What is the necessity for doing it? If you want an object to have all the featrures of a class + something more or something less, all you need to do is create another class inheriting the other. To incorporate this we have inheritance, ain't it?I don't think you can incorporate any further functionality to an object apart from the ones defined in the class.

overload the functions

Use Strategy Pattern

I think through Inheritance you can make use of Polymorphism to acquire multiple objects of same cadre but carrying different behaviour on events.

Functionality of an object can be changed by changing the property or attribute value

By using the concept of virtual functions, if you consider a class as an abstract class, we can override all the methods in its derived class, hence each of the objects of derived objects can have seperate functionalities.

class MyClass { 

We may forget, the question is really talking about objects of same class. So I think all the answer on virtual functions are wrong.tehoclubmay get close to the point of the question in my opinion.