FIA clarifies new engine rules
Charlie Whiting told 'autosport', "I think there's enough in the parc ferme rules to say that you couldn't change an engine after qualifying starts, although of course now if you had to, there's no penalty associated with it." Meaning that teams will only be allowed to change an engine if there is a proven problem.
This move essentially deters teams from swapping engines between qualification and the race, with the intent of using a fresher unit in the latter. Seeing how all Formula One teams are required to use no more than eight power units during the season, with a penalty given for the ninth, teams were originally figuring out ways for the restriction to have less of an impact on performance, such as changing engines between individual events within a GP weekend. But that has now been nixed.