(United States) After the convention but before the election, can the President nominee swap out their VP pick?

So our presidential nominee for the Purple party picks a VP, but after securing the nomination for the party, decides they didn't like their VP pick after all. What's the deadline to change their mind? The party is itself a private organization so while it might be against the party's rules, you might still be able to swap the pick. But after submitting the names to the states to get on the ballot, is it possible then to swap picks? After the election but before results?