Can an expired dual-occupancy approval be renewed or extended?

Yes, in limited circumstances. A Development Approval generally lasts for 5 years after it takes effect. An application to extend the approval can be made within 6 months after the end of that 5-year period, but the development must have started and substantially progressed, and the development would still need to be approvable if a DA were lodged at the time of the extension application.

Extensions can be granted more than once, but generally for a combined maximum of 2 additional years.

If the development has not started and substantially progressed, this extension pathway would not satisfy the stated requirements, and a new DA would generally be needed to proceed.

Reference: ACT Possible Outcomes - https://www.planning.act.gov.au/applications-and-assessments/development-applications/after-you-apply/possible-outcomes