Article II, section 1, pp 4: “The Congress may determine the Time of chusing the Electors, and the Day on which they shall give their Votes; which Day shall be the same throughout the United States.”
For a State to chose an Elector on any day other than the one appointed by Congress is specifically Unconstitutional. They have to stick with whomever they’ve chosen on the appointed day.
What if an Elector dies?
But Baca, the plaintiff, could have used your ideas