To be a CA/GRO you need to either hold or have held within the last 10 years an ATC or FSO Licence. That would pretty much count out most (if not all) ex-FSO's who didn't transfer to ATC
FWIW I believe once granted, unless suspended or cancelled by CASA, one is considered to
hold an ATC or FSO licence for life, irrespective of duties. It's just that the licence is not
valid/current without a current rating/endorsement or current medical.
MOS Part 65 somewhere. Same as doctors I guess. Once trained and qualified, you are a doctor for life, though not necessarily current or fully competent
dexta
The fundamental thing is that CASR Part 139 prevents an aerodrome operator from operating an air/ground radio service unless it is a CAGRS. One of the functions of a CAGRS is to provide advice of relevant air traffic.
Under MOS 139 a UNICOM is not permitted to provide that advice. For specific trials of UNICOMs in the past, CASA had to grant exemptions to allow limited traffic advice.
With the specific example you quote, MOS 139 would suggest neither would be permitted by a UNICOM:
14.4.1.3 Participation in Unicom services by an aerodrome operator, whether for the purposes of a frequency confirmation system or otherwise, is to be limited to the exchange of radio messages concerning:
(a) confirmation of the CTAF/MBZ frequency selected by aircraft;
(b) general aerodrome weather reports;
(c) aerodrome information;
(d) estimated times of arrival and departure;
(e) passenger requirements;
(f) aircraft refuelling arrangements;
(g) maintenance and servicing of aircraft including the ordering of urgently required parts;
(h) unscheduled landings by aircraft.