Well answered oldpinger, you may sit down.
Gezzill,
nope, nahdah, zip, not implying anything just trying to get you to see the answer to your own question.
Your preference, for pilot, is what you go to PSA for but they are selecting pilots for the ADF, so if your pref is for RAAF it does not mean they do not consider you for ARA or RAN.
As far as having a 1st pref for pilot and a 2nd pref for something non hands on controls, PSA is selecting you for pilot as stated by Shonfield. Speak to the DFR. I am sure they would be more than happy for you to have one pref as I am sure they would be more than happy if you did not make that one and came back and did another or had multiple pref. Remeber if you get in they make money.