If you were a Sharingan user, and you unlocked the Rinnegan (as Madara did), you would retain all the abilities you held prior to activation. Removing your Sharingan and implanting a pair of Rinnegan, however, would lead to you losing the abilities of the Copy Wheel Eye - you would only have Rinnegan powers, like Nagato.
No you still keep your Sharingan abilities when you unlock the Rinnegan,however if you transplant the Rinnegan eyes then the Sharingan powers are gone.