Preference change
Hi Numbersguy,
You are able to change your preferences at any stage up until the recommended/not-recommended part of the OSB, you probably already knew this.
I changed my preferences during the OSB, which probably didn't look good and they did ask me several questions regarding the change. I was truthful with the board, so I felt it went as well as it could've.
I don't think a preference change to RAAF ACO (replacing Army pilot) would look that bad at all, especially at this early stage! Although the board may ask you why wouldn't consider being an Army pilot. As long as you can justify it, it should be fine!
That's my opinion anyway.
Elliot.