One way around this issue of responsibility passing to the OC when a lot is sold in NSW would be to accept that the alteration is now the OC responsibility but when the new owner asks for it to be maintained because it’s common property is to tell the new owner that we won’t maintain it but we will remove it (at OC cost reluctantly). This would work for a/c installs and other additions to the lot because the owner is claiming it’s common property and so the OC have every right to remove it and restore the area to it’s original condition.
How many new owners who thought they could have unlimited maintenance on their unapproved additions only to discover that the only option that the OC will consider is removal.