GPA = Grade Point Average, u get 4.0 for a Pass, 5.0 for distinction...or something like that.
But as for the law transfer it is indeed possible, my friend got UAI in 70s and did economics at UWS penrith in the first semester of 2004, he transfered to Law/social science at Parra UWS and started doing it in the 2nd semester of 2004.
Mind you he did get something crazy like distinction-high distinction average, but he was told that he only needed a credit average.