Michael HR- I do not think Nicholas could have arbitrarily change the laws of succession. He was archly conservative and indecisive. Legally, it may have taken the council, Church, law courts and Duma to do so. This is one reason why his abdication for Alexei is considered by some to have been illegal.
As for other least favourite monarchs, I would put Leopold II at the top of my list, [butcher of the Congo]. Bokassa of Central Africa, Henry VIII, George IV, just for a start.