The Novikov Principle does not allow a time traveller to change
the past in any way at all, but it does allow them to affect
past events in a way that produces no inconsistencies—for example, a time traveller could rescue people from a disaster, and replace them with realistic corpses if history recorded that bodies of victims had been found. Provided that the rescuees were not known to have survived prior to the date that the time traveler stepped into the time machine (perhaps because they were taken forward in time to a later date, or because their identities were hidden), the time traveler's motivation to travel back in time and save them will be preserved. In this example, it must always have been true that the people were rescued by a time traveller and replaced with realistic corpses, and there would be no "original" history where they were actually killed, since the notion of "changing" the past is deemed impossible by the self-consistency principle.