I don't think doing the online tests twice gives anyone and advantage. Once you get to the assessment day, you will be assessed by at least 7 different people, and possibly more (who knows what they remember about you as you hoe into the free sandwiches at lunch time and chat to the assessors). That's where you have to shine
When it gets right down to it, you either have it or you don't. In the long run, it may be better to be knocked out in the early stages of selection than to move to Melbourne and flunk out of the training course.
In some ways, (and I really don't want to upset any unsuccessful applicants here) selection is a bit like auditioning for Australian Idol. Your life's ambition might be to work in ATC (be a famous singer), but you might not have what it takes (be tone deaf).
Don't forget, if you do get selected you may not get through the training. I've already be alerted to the fact I may not finish the training because I'm an old fart at 47.
Oh, and if you think the selection process is tough, wait till you start dealing with CASA.