I think you don't understand the Australian voting process very well. Australians are not as accepting of robocalls as Americans are (and with mobile phones becoming the norm, robocalls get expensive); the voting date is hard to fake since everyone has to vote at the same time and there are media blitzes about the date itself; and polling addresses are meaningless, because if you don't go to one of the ones for your electorate, you can go into a polling station anywhere in the country and record a vote, it just takes marginally longer. If you try and make it so that voters have to queue for 8 hours to lodge a vote in order to marginalise them, people will give up and go to another polling station. People here complain bitterly if they have to wait an hour to vote.
If someone did try the voting date switcheroo and succeeded in stopping a sizeable portion of people from voting, the most likely outcome - apart from the scandal - would be that the Australian Electoral Commission would call for a repeat of the voting for that electorate. By-elections happen all the time; it's not something that would be procedurally unusual.
Blackmail is still an option though, and still a good reason to oppose the law.