It appears that the Manga is saying that both the Sharingans and the Rinnegans were transplanted. If this is not a mistranslation, then, How is Madara getting more rinnegans?
it appears that he can now evolve Sharingans into rinnegans at will. He must have some way of maintaining control, perhaps there is a huge chakra rod inside the Body of the Jinchuurikis.
Even if he were using sharingan control, this is still a risky proposition vis a vis Kabuto.