This is irrelevant, my question is can you enter/depart as "crew" if you are in fact not "crew"?
Yes, if you have an Oz/Nz passport nothing further is required (except technically a letter from your employer if positioning inbound stating your date of exit). If you dont have a Oz/Nz passport, you are to have a Crew Travel Authority (CTA).
https://www.immi.gov.au/skilled/air-sea/air.htm
Document requirements
After registering with a CTA, crew are still required to hold the appropriate documentation to facilitate processing on arrival. The document requirements will vary depending on the position a crew member holds.
Operational crew
Operational crew (entering as a crew member and departing as crew or a passenger) must hold:
a valid passport
an Airline Identity Card
and
for freight only – should be issued with a CTA and be listed on the General Declaration Form signed on behalf of the air carrier.
Positioning crew
Positioning crew (entering as a passenger and departing as a member of the crew within 5 days) must hold:
a valid passport
and
a letter from the employer certifying that the person is an aircrew member, setting out the purpose of travel and the arrangements for the person to leave Australia.
Aircraft Safety Inspectors
Aircraft Safety Inspectors, who are treated in the same manner as crew when engaged on inspection duties, must present:
a valid passport
either a valid government identity document showing that the person is employed by a foreign government
or
an ICAO Safety Inspector Certificate.