ActionScript 3.0 :: Redefining A Function On The Fly?

I have a method/function inside my class called "doSomething()". This function gets called once a frame.

I am trying to figure out if it's possible to redefine that function on the fly with code.

For example, For the first 100 frames of my move I want "doSomething()" to look something like this :

Code:
public function doSelected():void {
trace("hello");
}

and then after 100 frames has passed I'd like "doSomething()" to be redefine to look like this :

Code:
public function doSelected():void {
trace("bye");
}