I tried animating the extends of a PhysBone Collider in a world (radius and height), but the animation only affects the initial state when loading into the world (given the animation is already running at that time). After that, the animation won't update anymore.
Changing the scale works, but that doesn't allow to change the height and radius of a Capsule independently, since non-uniform scale is still applied uniformly. I'm not sure if it is simply considered a not supported feature, but since the fields are animatable I just thought it would work.
Note that my attempts to animate those properties where merely an attempted workaround for the non-existing Udon access so far. See canny: https://feedback.vrchat.com/udon/p/expose-physbone-collider-vrcphysbonecollider-to-udon