Other:
In an extreme and immediate case I would instantly act against the Australian constitution, in the hopes that later a referendum could be put to the people ratifying or disapproving of my action once the threat has been dealt with. If the Australian people believe that my actions were unjust or 'un-Australian' as it were, I would face the trial and jail sentence for my actions.
If the case was extreme, but not immediate, I would act through the proper institutions, going so far as to attempt to be elected to Parliament, in an effort to have a referendum put to the Australian people to meet the threat that caused my concern.
In all other cases, any area dealing with a constitutional amendment or acting against the constitution is illegal. A reasonable section of the Australian Constitution is dedicated to the various ways in which alterations to the Australian constitution could be made.
Lastly, there is always the chance that I would just move to New Zealand, Wales, Scotland, Canada, N. Ireland, Ireland or the US of A if I saw no way of dealing with what-ever issue I have that the constitution disagrees with.
Whoa... Can't believe these forums are still kicking.