Yeah...I’m no law scholar...but I’ve never read about any powers given to the FBI to make laws.
Neither have a Constitutional basis when they start negating arbitrarily parts of the Bill of Rights.
"Valerie Caproni, the FBI general counsel, said the bureau had fixed the problems with the national security letters and had taken steps to make sure they would not recur. She also said the bureau -- which does not need permission to alter its manual so long as the rules fit within broad guidelines issued by the attorney general -- had carefully weighed the risks and the benefits of each change."
They're weighing the benefit of violating our 4th Amendment rights against unlawful search and seizure against the risk of getting caught and being held responsible. It looks like they feel confident in their ability to succeed.