You can try to transfer but as D94 said, it's still quite competitive - recommend atar over 97 and D average. You may need higher than that though, just depends on the competition.
However combined law isn't the only way to do law. You can do an undergrad degree in whatever you want, then apply the Juris Doctor post grad. The JD takes 3 years, so it's only one more year all up for both degrees than it is doing a 5 yr combined degree. There is also no difference in how employers treat JD students to combined law students - you have the same degree in essence (the only real difference in my opinion is the name). You can do the JD at many uni's now including USYD, unsw etc You should look into it if you really want to do law (if you don't get into combined or can't transfer)
there are lots of options out there to study law.