The Government Communications Security Bureau has so far implemented 25 changes recommended in the Kitteridge report, Prime Minister John Key says.
Cabinet Secretary Rebecca Kitteridge investigated the spy agency and concluded it may have illegally spied on 88 New Zealanders.
She recommended 80 changes and the Government decided it should implement 76 of them.
Mr Key says the changes put in place so far include appointing senior staff including an associate director and a chief legal adviser.
The agency's previous chief legal adviser, Hugh Wolfensohn, resigned amid the controversy over potentially illegal spying.
The GCSB had believed it was acting within the law when it helped the Security Intelligence Service and the police spy on New Zealanders, but there was a clause in its legislation which said it couldn't do that.
Arguments raged over the legal interpretation of the legislation, and there are still differences of opinion.
Mr Key says the GCSB has established new processes and systems across its legal and compliance frameworks.
"The GCSB is under no illusion that bringing about change and regaining public trust will take some time and effort."
Mr Key says 11 more changes are on track to be implemented during the next quarter while some could take well into next year.
He announced on Monday he had appointed former High Court judge Andrew McGechan as Inspector-General of Intelligence and Security, taking on the oversight role of the GCSB and the SIS.
He has replaced Paul Neazor, who didn't want another term.
Mr Neazor investigated the 88 cases of potentially illegal spying identified by Ms Kitteridge, and concluded the agency had acted within the law.
His finding was controversial but Mr Key says his replacement won't review it.