No, in the Spell area in the unit editor, there is a ability called Sphere under special in human. The Sphere is an invisible ability on the blood mage that gives him the spheres, if you change the old blood mage attach model: sphere to let's say, a footman, the bloodmage would have footman flying around his head, this works with all the models, arrows, buildings etc. You can also make another sphere ability and change it instead of overwriting the other sphere spell, just make sure to give the blood mage the new one and not the old.