The Nuclear Non-Proliferation Treaty (NPT) forbids any of it signatories to have nuclear weapons. Full stop.
Under the terms of the NPT, the P5+1 have no legal authority to amend the treaty unilaterally, to abrogate the treaty, or to allow nations that are signatories to the NPT to abrogate the treaty.
Since when can the UN Security Council amend U.S. treaty law? The UN can certainly propose amendments, but it cannot approve such changes on behalf of the U.S. Congress and the American people.
If Iran is allowed nuclear weapons capability, other nations — especially throughout South America, already infiltrated by Iran — will doubtless follow suit.
In Iran, would this agreement have the force of law, or would the Supreme Leader — who just this week said, “Death to America” — be allowed to change its terms unilaterally? And what would be the consequences to him if he did?