It can’t be if I understand both the US and the state constitutions. Legislatures are the final word on selecting electors, can do so with or without any “certification” by anyone.
Also, in 1864, half the country’s electors were out of the Union, so they took the majority of those states remaining.
Not worried about switched votes, just delaying the vote which creates an appearance of uncertainty about the election. Fortunately, America left and right was tired of the campaign and grateful for the end of this cycle.