Update sun position without reading entire octree file again?

I have a ridiculously large model (with lots of octree instancing) that I need to render for a large number of sun positions. It takes several minutes to read in the octree, after which the rendering itself is quite fast. Is there any way to read in the octree file just once and then create multiple renderings with different sun positions? I’m thinking like the rpict -S option, except changing the sun/sky definition instead of the camera position.

You could use rcontrib. Include all the suns in the octree, but each with a
different modifier name. Then pass the list of modifier names to rcontrib
with the -M option.