Mark Saunders was shot dead in a siege in May 2008
Firearms officers should not confer with each other before writing up their accounts of shootings, according to senior police officers.
The Association of Chief Police Officers (Acpo) said there was no need for officers to compare notes.
But Acpo stopped short of banning the practice, saying officers should note any discussions that do take place.
The Independent Police Complaints Commission (IPCC) said police had acted upon its calls to end the practice.
Senior officers agreed to look at the issue after a case was brought by the family of barrister Mark Saunders, who was shot dead at his Chelsea home in May.
His sister Charlotte went to the High Court to argue an independent investigation had been unlawful because officers had conferred on their notes.
The case failed, but Mr Justice Underhill ruled the principle was "highly vulnerable" to being challenged under the Human Rights Act.
The judge described conferring as an institutionalised "opportunity for collusion", but conceded that banning it could hinder investigations.
Ms Saunders welcomed Acpo's decision to change its guidelines.
She said: "Although we cannot undo the damage that may have been done by allowing officers to confer to date, this change means that the IPCC can focus on being more independent and thorough for the remainder of Mark's investigation."
Her solicitor, Jane Deighton, said: "Charlotte's persistence has won through and deserves respect."
The IPCC first raised objections in its 2006 report into the shooting of Harry Stanley, when officers mistook a table leg he was carrying for a shotgun.
It said the practice risked accusations of collusion, potentially prejudicing any inquiry into the incident and damaging public confidence.
Similar criticisms were made in a report into the shooting of Jean Charles de Menezes in July 2005.
IPCC chairman Nick Hardwick said: "We believe these changes are in the best interests of families, police officers themselves and the wider public.
"There is still some work to do to finalise the relevant operational procedures but the IPCC will now reflect these changes in its investigations into future fatal police shootings with immediate effect."
Acpo's decisions to revise its guidelines came as one of the officers who shot Mr de Menezes gave evidence in public for the first time at the inquest into his death.
Chief Constable Meredydd Hughes, Acpo lead on uniformed operations, said it was a "difficult and complex issue" for the police and that the revised guidelines would take time to implement.
The revised guidelines said firearms officers should ensure all activity relating to the recording of accounts was open and transparent.
However, Paul Davis, of the Police Federation, said "conferring before making notes is a long established practice intended to achieve best evidence and ensure accuracy".
Mr Davis said the federation had consulted with Acpo and added: "We have made clear our view that, if there is to be any change to their guidance following deaths in police contact, officers must still be able to confer should they consider the circumstances require it in a particular case."