Everything is possible programmatically.
You can just set the wind and gravity values on the physics constraints directly. If you key the physics constraints' wind and gravity, you'd need to modify the values after you apply animations.
If you would rather use an animation, you'd have to create a new animation and timelines or dig through an existing animation's timelines to find the wind and gravity timelines, then you can change the keyed values, add/delete keys, etc on the wind and gravity timelines. Note that by default the animations are shared by all skeleton instances, so you'd need to duplicate the animation if you don't want your changes to affect other skeleton instances.