Dennis Swanson has been Mr. Presto Change-o since mid-July, when the industry was shocked to learn he was “retiring” as general manager of immensely profitable WNBC-TV in New York. The industry was stunned to learn only three days later that Mr. Swanson was not retiring at all but instead was the new chief operating officer of the Viacom Television Stations Group, which included CBS stations still paying the price of former owner Larry Tisch’s penny-pinching.