Whether or not he actually controls every single cell has not been discussed in the manga, so it cannot be inferred that he has manual control of his cells when healing him wounds. It has never been shown that medical ninja control the healing at the cellular level either, but by reconnecting blood vassals and whatnot.
However, let's assume your theory is correct that Hashirama does in fact control every individual cell in his body. Even if this were true, what does that have to do with him breaking the edo tensei bond? His cells strengthen the bond Orochimaru has over him, and to infer that the opposite also holds seems unplausible.
Let me give you an example: Assume the bond is by a rope. Now let's assume Hashirama's cells applied to the rope increases the strength of the rope. Does it seem logical, then, to claim that Hashirama has better control over the rope? No, because the rope has been infused with his power. You can't counter with an argument of the form: well now he controls the rope. That's like saying Naruto or the Kyuubi automatically have control over the Gold & Silver brothers.