Whats the best way to get a non-aus id? And what are the drawbacks?
You have to create an entirely new PSN ID. Simple process to make one, but it's whether you'll commit to the new account or switch between it and your existing one so you can still use your old purchases.
For the Vita, you'll need either a separate memory card or format your current one to use a new account on it. You also have to format your system itself to associate a new PSN ID with it.
I did it because I had very little in the way of digital purchases. Only major loss for me was my actual "Aytrial" PSN ID.