Box2D or Chipmunk physics, how do I shrink or grow a shape?

[RedHades]

I'm trying to figure out how to increase the diameter of a circle shape during gameplay.
I've checked the examples for both Box2D or Chipmunk extensions, and I understand how you create a new circle shape with a specified size parameter. But I can't figure out if there a way to change that size later after the shape was created.
I want to make something like a ball that shrinks and grows.

This is kind'a urgent since I'm experimenting for a 48 hours game jam.

[Looki]

In Box2D you'll have to create a new shape and remove the old one, I don't think there's a better way.

[KLiK-iT]

There is no better way. You just can't re-size the shape and have it act like the original as far I know. I never tried this,.but what about an animation for the ball? One that goes from big to small and the other small to big? Worth a try!

[RedHades]

Yeah that's pretty much what I ended up doing and it worked well enough. Thanks.