The skybox is actually an axiom object which makes it a little harder to manipulate .
But it looks like the skybox is a scene node called SkyBoxNode so you may be able to retrieve it from the axiom scenemanger, but by default it will not be added to the multiverse nodeDictionary so you cannot use the normal ClientAPI.World.GetObjectByName() function. You might be able to grab it from python using ClientAPI._sceneManager.GetSceneNode("SkyBoxNode") and then applying the orientation normally.