I dunno....I don't think they can bypass the delegate process, but we'll have to see. I can't seem to find anything in federal election law, presidential, relating to post party nomination acceptance withdrawl. (sounds like a temporary neurosis, doesn't it?)
Until the candidates are placed on the ballot election law does not apply, only the Constituional requirements. In the case of Eagleton and Shriver in 72 the DNC met and made the choice of Shriver which was honored by all 50 states. Remember that federal election law is limited. The Constitution gives to the legislatures of the several states the duty of choosing the means for selecting electors. The Constitution apportions electoral votes per state, but the states decide how to apply them. Two states, Maine and one other give the winner the two electoral votes representing the senators and apportion the remainde by who won the congressional districts.