Raikatsu had used his regeneration to attach the rinnegan to his eye fully, then used his mental reaction timing to speed up the recovery. He did not have full acess to all his techniques though. He then got a marvelous idea from a jutsu he knew. Izanagi. He cast the jutsu and turned his sharingan eye into a rinnegan, making himself have been born with rinnegan, altering history. However it was a solo alteration. He also did one other thing, he allowed his rinnegan to keep his EMS justu. The man was called a genuis for a reason. He didnt even have to lose his eye to do this, due to him being born with rinnegan, it was the brilliant part.