Sorry - that isn't clear to me. You show 'Class B' indented under A but then you also show an INNER 'Class B'.
Is B an inner class of A? Is C an inner class of B?
What does 'without disturbing the code in Class A' mean? If you modify an inner clause then, by definition, you are modifying the outer class.
What does 'so I can use class C with new properties' mean? Use it where? As said above if C is an inner class then it is PART OF its containing class. Any change to C automatically changes A since C is a part of A.
What PROBLEM are you trying to solve. You have tried to tell us the solution you want to use but we need to know the problem.