then an EO is required (what a rort)
Unfortunately CASA is going down the EASA path rather than the USA's FAR's where the approval path for a minor change is very straightforward and there is an appropriate progression in rigour as the task becomes more complex and broader in nature - the 337 (I note the criticism of 337s but thats a result of people abusing the process rather than following the process as defined by the FAA) and the STC. Here, per the new CAAP 35-7:
According to the regulations, all repairs and modifications, major or minor, to Australian registered aircraft must be approved.
"All" means "all" and the approval required is per Reg 35.
It should be easier for minor stuff but my guess is that it won't get any easier with the new suite of regulations.