The Constitution (Article 2, section 1) is silent on this issue so the selection of the electors is paramount. It would therefore also be constitutional for a state legislature to impose a fidelity to the popular vote oath.
Maybe If the little district judge blocks it and many months later the SCOTUS happens to not be too timid to rule, and doesn't take off on another recess vacation and wait July,2021 to rule "maybe."
Colorado imposed such a law, and the Court has thrown it out.
Obviously, I’m in the minority here, but the decision is consistent with the doctrine of original intent.
Amendment 12 says that the electors sign the lists; it does not say that they sign the ballots. The best I can show you right now is this:
https://scholarship.law.gwu.edu/cgi/viewcontent.cgi?article=1627&context=faculty_publications
Therein the Tennessee list was filled out correctly, and the Georgia list was not quite. (For the record I think it was properly counted for Jefferson and Burr) Ideally we need a split delegation vote to really demonstrate the point (only such delegation was Rhode Island that year).
Aha!
https://elections.lib.tufts.edu/catalog/tufts:us.potus.1800
So no the ballots weren’t signed, just the lists.
The obligation is with the parties to run loyal electors.
I am also of the opinion that former President of the United States is an office of trust or profit of the United States (pension, secret service) and Bill Clinton was ineligible to serve as elector. I was inclined to think that just his vote should have been disqualified but after rereading the Virginia Law Review article, I think the entire New York vote should have been disqualified.