Nope. Pacers have to race from the start, hence why the pacers for lead men and women often drop out between the halfway mark and 20 miles, depending on their fitness and endurance level. Pacers for the masses are different, those are expected to run the whole thing and are generally runners who can comfortably cover the distance in a faster time than what their pacing.

The one exception to this was Kipchoge's 1:59 marathon, where pacers rotated in an out, and that's one of the several reasons why it isn't an official world record.