Can I change the building certifier during construction?

Yes. A landowner can change the building certifier after construction has started. The Building Act 2004 specifically allows an eligible certifier to be appointed where building work has already begun, provided the work has been carried out in accordance with the relevant requirements.

The landowner, not the builder, is responsible for appointing the certifier. The existing appointment must be properly ended and a suitably licensed replacement certifier appointed to take over the certification and inspection responsibilities for the remaining work.

Reference: Building Act 2004(2004-11), Sections 19A and 19D - https://www.legislation.act.gov.au/View/a/2004-11/current/html/2004-11.html