If a person were interested in taking an entirely different position on human rights, the guardian council that vets the candidates would never allow such a person to run. In any case, even if such a person were to run and win, the Supreme Leader has complete authority to overrule and dismiss the president. The judiciary has established itself as a very powerful organ that can broadly interpret laws, like insulting Islam, to do whatever they want, and the Revolutionary Guard Corps pays little attention to what the president does.
So the scope of reform within the framework of the existing system is depressingly small. That is one reason why a great many Iranians are interested only in the three-metre circle around them. On the other hand, we have a Supreme Leader who is terrified of the prospect of a Velvet Revolution.
In the Velvet Revolution in Czechoslovakia, Mr. Havel was a dissident with seemingly no prospects of ever having any political post on a Thursday morning, and on the Tuesday morning he was the President of Czechoslovakia. It all happened in less than a week. Indeed, one week after the start of the Velvet Revolution, Mr. Havel was in the White House. I presume the Supreme Leader knows something about his country and worries about this.