Professor John McNeill said he no longer insists on certain recommendations he made in the report, published in April.
In a letter to Strathclyde Police Deputy Chief Constable Campbell Corrigan, he offered a "sincere apology" for the mistake.
The report criticised the force for the way it handled complaints from a driver who was pursued by an unmarked police car on a motorway for seven miles in January last year.
The man called 999 from his car - to learn he was being followed by a squad car.
The report recommended that the force apologise to the man for being stopped by the plain-clothes officers, who, it said, had no power to do so.
Prof McNeill said he still considers the pursuit of the car to be "highly inappropriate" but now accepts that his interpretation of the law in relation to a plain-clothes officer's power to stop a car was wrong.
He said it was appropriate for him to publicly acknowledge the error.
Prof McNeill said he no longer insists that an apology be issued to the complainer.