The harsh e-mail from President of CBS News David Rhodes about the network’s “bad Monday morning” augurs of dramatic changes to come, sources say. “There will be a big shakeup on news when Katie Couric leaves in the summer,” a source told us. “Scott Pelley is already telling people that he has landed Couric’s job.” Another added that “The Early Show” executive producer David Friedman, who was among those lambasted by Rhodes yesterday in a department-wide e-mail barking “Let’s get with it,” is already looking for a new job. A CBS rep declined to comment.