Yes. You may choose not to be Commonwealth supported for any of your units of study. In order to do so, you must inform an appropriate officer of your higher education provider, in writing, on or before the census date that you do not wish to be Commonwealth supported in relation to the unit.
However, you need to be aware that, subject to fairness requirements under the Higher Education Support Act 2003, your provider is under no obligation to offer you a fee-paying place for those units. You also need to keep in mind the benefits associated with being Commonwealth supported.