The "claim of right" defence used in the Waihopai case will in future have to satisfy a property-right test, but not a reasonableness test.
The Government yesterday issued its decision, approved by the Cabinet this week, on its review of the defence, which was used by three activists who slashed an inflatable dome covering a satellite dish at the Government Communications Security Bureau base at Waihopai.
They were acquitted by a jury after arguing they believed their actions had disrupted intelligence communications and saved lives in Iraq.
But under the changes announced yesterday, they would not have been able to use the defence unless they proved they owned or possessed the property.
"Adding a property right criterion means the defence will be available only to defendants who believed they have a proprietary or possessory right in the property involved," Justice Minister Simon Power said.
"As the law stands, defendants charged with certain property offences can use the defence if they genuinely believe their actions are lawful.
"But it's clear that the defence was not intended to be used to excuse people who take or damage property who are not claiming a personal property right, as in the Waihopai case."
Mr Power said the amended law would still recognise that defendants who made an honest mistake should not necessarily be criminally responsible for their actions.
The Government rejected the other options for reforming the law, including adding a reasonableness test or repealing the law.
The defence, which can be used in 14 property offences, rests on a belief that a person has the right to somebody else's property, even if that belief is mistaken or unreasonable.
The belief must be honestly held and of legal, not moral, entitlement.
Green Party human rights spokesman Keith Locke said it was dangerous to change the law because the Government disagreed with a court verdict.
He said the change would mean a person could not break into a house to save someone screaming for help, or take someone's car from them because they were drunk.
But the convenor of the Law Society's criminal law subcommittee, Jonathan Krebs said such examples were not valid, as other defences applied, such as a duty to preserve human life.
He said the society did not believe the law needed to be changed.