I don't think impersonation of a reporter would ever be considered illegal (as opposed to say impersonating a police officer). In the best/worst case, the evidence obtained would be deemed inadmissible. Once that happened, the FBI and other police would be less-inclined to employ the ruse. That would be the remedy that would help the press. Short of excluding the evidence, there is no other remedy I can think of that would help the AP in this instance.