graphicnovel, "I don´t think I´d have the patience for both ways doh...."

Even if you did five total rerenderings, going through all the trouble with resetting light and shadows, changing most of the material between each and have to make new normal and displacement maps as well as taking into account occlusion, specularity, etc etc.

Even if you did all this you would not even get close to all the work the old masters did before they began to paint the final painting.