Yes. There's been rogue electors in the past who have voted for the other candidate. Some states have laws that punish electors who do this...but such punishment would be after-the-fact, and there's some question as to whether these laws are even constitutional, i.e. whether the state has the power infringe upon the elector's powers.
Yes but doesn't the Secretary of State have to certify the election? If the electors go rogue, the SOS might just refuse to certify the election for that state.