Some less strongly typed languages let you change the parent class of an an object at runtime. I was just reading about this yesterday in ECMAScript aka JScript where you can change the template (parent class) on the fly.
THIS ARTICLE claims to do dynamic inheritance in Java but it's just using a Factory Method and not changing anything about a given object instance.
We can get more dynamic behavior through delegation and swapping strategies at runtime, but it's still not really changing the parent class.
A good question is never answered. It is not a bolt to be tightened into place but a seed to be planted and to bear more seed toward the hope of greening the landscape of the idea. John Ciardi