Even when Forrest Sawyer is sitting in, it's still World News Tonight With Peter Jennings . Just because Johnny goes on vacation, The Tonight Show Starring Johnny Carson doesn't suddenly become The Tonight Show With Jay Leno . The task of a guest host is delicate.
It doesn't matter who the anchor is, the program is still World News Tonight with Peter Jennings.  
The shows will change names depending on who is sitting in at the time.  