Board Thread:Naruto Discussions/@comment-24824859-20150716001406/@comment-4912646-20150716003714

UltimaDude wrote: I'm a bit confused as to how Kabuto modified Madara's body? I mean, didn't he have Wood Release and the Hashi-face before he died? Can somebody please help me understand? It wasn't explained very well, but here's what we know:
 * Kabuto told Madara that his Edo Tensei was special. This may be intended to explain why he was revived as his younger self or it may simply refer to the fact that Kabuto implanted Hashirama cells in his body. Unfortunately, it's never mentioned again after Madara's initial resurrection so we don't know.
 * Kabuto admits he did not know that Madara survived the Valley of the End battle or that he awakened the Rinnegan before his death. Through this it can be inferred that Madara was likely reincarnated without the Hashirama cells implanted in his chest, which would mean he essentially awakened the Rinnegan for a second time (though this time it didn't take decades).
 * Lastly, Madara tells Hashirama that the face on his chest is a result of his subordinate's comrade's (Kabuto's) modifications, not his own. He says Kabuto just happened to have the same idea as him, again implying that he was reincarnated without any Hashirama cells. Kabuto also noted that what he did to Madara was beyond what Orochimaru did with Danzō, but didn't elaborate on this statement.

So from my understanding, Madara was revived as he was during his final battle with Hashirama, meaning he lacked Hashirama's cells and the Rinnegan. Kabuto implanted Hashirama cells into his reincarnated body because he and Orochimaru had hypothesised that this would awaken the Rinnegan, and he was correct. Why Madara was revived as his Valley of the End self without any of his later modifications was never explained.