Import both reference object geometries into Poser. Delete sea dragon body, then move head onto milldragon head until it fits. Delete milldragon head and redo hierarchy. Export new object file to reference folder. Edit milldragon.cr2 to point to new reference geom. This method has alot of gaps in it, but it might work. The experts can tell you the entire, tedious procedure if it doesn't work, assuming you have a vertex modeller of some kind.