Yes, it is definitely possible to appoint or remove officeholders and directors after company registration, however you must directly notify ASIC of any changes within 28 days of the appointment or removal.
There is a specific process that you must follow to lodge these updates with ASIC. First, you must use the company's corporate key (an 8-digit number generated by ASIC within 10 days of company registration and posted to the company's registered office address) to create an ASIC Officeholders account. Please follow the link to set up this account: http://asic.gov.au/online-services/register-for-online-access/company-officeholders/
From within that account you will need to submit an electronic Form 484 to appoint/remove officeholders and shareholders.
If you require assistance to navigate this account then please contact ASIC's customer service team on 1300 300 630.