While doing something about the issue might be warranted, I’d like to point out that it’s the BCA/NCC building codes (at the time of construction) that the OC needed to meet.
If the BCA/NCC codes were met, then changes to the construction are optional. I doubt that any Tribunal in Australia would rule otherwise.
If it can be established that the construction did not meet the BCA/NCC building codes (at the time of the construction) the result can be very different.
Else get enough owners on board and get things changed.