A system and method are disclosed for modifying a television broadcast signal. In one embodiment, the system includes a memory that stores an alternate commercial signal, and a controller that is coupled to the memory and receives the broadcast signal. The broadcast signal includes a program signal and commercial signals. The controller substitutes the alternate commercial signal for one of the commercial signals upon determining that a first condition has been met, for example, upon the sensing two video/audio blank periods in the broadcast signal separated by a predetermined time period. In another embodiment, a broadcast signal including a series of screen signals alternating with a series of blanking signals is embedded, at an upstream location, with additional information relating to alternate commercials or commands during the blanking signals. At a downstream location, a controller processes the additional information and modifies the broadcast signal in response.