Article II says state legislatures have the power to direct how presidential electors are appointed. They chose to have the voters in the states choose them. Can the legislature change the manner in which electors are selected? Of course they can. Can they do it after the electors have already been chosen? Maybe, maybe not. The courts would have to decide that.
Post 14- I disagree. Moving the goal posts is just not in my definition of a fair game.
Yes, the legislature change rules before the election, but on game day, there is only one set of rules. Period.