Board Thread:Theories and Speculation/@comment-1512913-20150221101637/@comment-24071637-20150222065600

Except users of Rinnegan that they did not originally own cannot switch their eyes' form. It's like they have those ad signs that have images on multiple sides and they turn to show a different ad, except their signs can't move so they only get to advertise(use) one side(Rinnegan). If they had a Rinnegan like Sasuke's we can assume they would be able to use both the Sharingan abilities as well as the Rinnegan abilities, as there is only one side, unlike Madara's.