javassist jbossretro

Hi,
I'm using ClassFile.renameClass as in jbossretro in order to replace instances of a class in a some.jar to my own class.
This is what I wants to achieve:
Some classes in the some.jar are using class A:
public class A {
....
}
I've created a new class AA:
public class AA extends A{
....(overwrite some methods)
}