It is possible to study at an overseas institution that UWA does not have an agreement. However, it's important you discuss your study plan as well as the standing and reputation of the overseas institution with your Student Advising Office in order to gain approval.
You will need approval before you go to be sure you will get the credit for the study you have done at the oversea institution.

If you are a domestic student you will be liable for all your tuition fees at the host overseas institution and these cannot be added to your HECS debt.

If you are an international student you will be liable for all your tuition fees at the host overseas institution.

You can learn more about overseas study  at Study Overseas. The Global Learning Office can give you some information about how best to go about applying for Independent Study Abroad but as no formal agreement exists and application procedures may vary from institution to institution, they cannot guide you throughout the entire process as they would an outbound exchange student.