At least in the primaries, when Pete Buwhatshisname and Pocahontes dropped out after some early voting people were not allowed to revoted if they’d voted early.
The electors are for a ticket. If the ticket changes then the votes are different. If it ceases to be a Biden/Harris and becomes, Harris/Whoever I would think they need a different set of electors.
It's true that the candidates vet the Elector list, but in modern elections the Electors are mainly party insiders who are often precinct captains or state party delegates.
Even if the candidates are replaced, the Electors will be the same party insiders, as there really aren't any others that the parties would assemble.
In Madison's and Hamilton's day (as laid out in Federalist #68), it may have been close confidants of the candidates or business and community leaders in the state who were chosen as Electors to make wise choices, but today it's tightly controlled by the state parties. They just can't be current office-holders.
-PJ