Hi,
As long as you keep the sky model into its own scene file (e.g. sky.rad), then it is easy to rotate it using xform.
For instance to rotate the sky 30 degrees towards the West which is equivalent of rotating the objects 30 degrees towards the East:
xfrom -rz 30 sky.rad >rotated_sky.rad
Of course you then also need to redo the octree
Raphael