It's illegal to import material into Australia that has been refused classification. You could be fined for it, although generally they'll likely just confiscate it.
I hope it isn't changed, slowly eroding the MA15+ restriction until it includes everything isn't a solution. It isn't up to the classifications board to decide on the issue, it's up to the states to appoint people who can be mature enough to uphold Australian laws and beliefs. That Atkinson found a loophole (he's stated in the past he doesn't like R18+ movies too, he just can't do anything about it) is disgusting, the Australian people just need to make more of a fuss about it than they already do.
Personally, I'm looking forward to a strong freedom of speech party starting up in South Australia. If the South Australian government can see that it's costing them votes having Atkinson there, he'll quietly be given a new portfolio and the new guy will be more reasonable.