Boy, go read the earlier chapters of the manga.. It clearly explained that the rikudou chakra is only born through people possessing the powers of BOTH the uchiha and the senju.
What you're talking about is invalid, because Madara NEEDED to inject HASHI_FUCCKING_RAMA'S CELLS a.k.a. SENJU CELLS INTO his BODY!
I think you don't understand the complexity of Hashirama's cells... The whole reason why his FACE appears on his chest is because the chakra level of Hashi's cells is extremely powerful to the point where it has manifested it's hardened core in the form of hashi's face, culminated in a single spot in Madara's chest.... Hashi's cells spreaded into Madara's body and MIXED with his cells, CREATING AND FORMING NEW CELLS, <----- and EVEN IF this is wrong, It's the same as Madara using his susanoo without his eyes after he came back to LIFE life.... When you unlock a power, you attain that skill forever... Madara didn't NECESSARILY need his eyes, which ISN'T chakra oragnically, to perform Susanoo.... Madara DOES NOT NEED HASHIRAMA'S FACE ON HIS CHEST, which IT itself, isn't chakra, to use his Rinnegan.