Enable “Use environment volume”, create a “Vray Sphere Fade Volume” material in the Hypershade and drope it into the Environment shader slot in the Render Globals. Then go to Create → Vray → Create VRaySphereFade.
Lets say I changed a characters t-shirt to jacket in an all ready renderd animation could you parent the spherefade to encompass the jacket area and render out just that section as it moves through the scene…