There's always subsequent rounds, and people shouldn't be changing their preferences unless their ATAR is seriously inconsistent with expectation anyway. Like, if Preference 1 published cutoff is 87 and your ATAR is 80, no reason to change it.
Peopl shouldn't really arrange your preferences strategically, you should just literally list the courses you want to do in the order you want to do them, especially for the first round. You never know what can happen 
See, whilst that's fair enough for going after something higher, I had difficulty because I wasn't sure if I wanted something
lower.
Quite ironically, now I'm now in the same thing I was debating against, i.e. computer science. And the debate literally started the day after ATAR release. Back in 2015, I got to have a full two weeks to end this debate with myself, and that would've rushed it heaps. I knew I wanted to do maths, but I was practically lost between whether I wanted actl or comp sci
And well, UNSW doesn't have late round offers for many degrees as well. Actuarial was one of them.
For all I know though, my scenario could've been an edge case