I think I understood what Eric is asking.
Of course if you use the same file lots of informations will be lost once you open it in moi again and save.
My solution is to have a separate .3dm file that you will use only with Rhino+Octane (eg. MyProject-Render.3dm); if you need to make any modifications to the model, you can use moi and then replace\add only the part that you changed into the render 3dm file.
M.