Formula 1's teams will run to new rules governing the use of engine power modes for the first time from Saturday's qualifying session at the Italian GP.
From now on, cars have to use the same single engine mode from the start of qualifying to the end of the race, whereas before drivers could switch between higher and lower settings.
It means that what have previously been dubbed 'party modes' - the top settings used for extra power at the end of qualifying, for instance - are now outlawed.
So what impact - if any - will it have on the pecking order?
Mercedes have dominated qualifying this season, taking all seven pole positions and five front-row lockouts in succession, and have regularly been able to increase their gap over the chasing pack from the end to Q2 to the pole-deciding Q3 phase by deploying their most powerful mode.
Sky F1's Jenson Button said: "It's a good thing - and it's going to bring everyone closer together.
"Teams like Mercedes have a better 'party mode' for qualifying so there will be a bigger shift, but it's not going to be enough to elevate the Red Bull up with them in qualifying.
"But it also makes the race a bit more interesting because Mercedes can't just go and turn the engine down when they get a good lead. They have to keep the same mode through the race."
With Mercedes thought to have the most powerful top mode among F1's four engine manufacturers, the expectation has been that they have more to lose than most where qualifying in particular is concerned.
However, neither the world champions' drivers nor management have been especially perturbed by the change - and even suggested they might gain relative to their rivals in the race.
"Clearly the engine mode was something that we performed particularly well on," said Mercedes team boss Toto Wolff to Sky Sports F1. "Having that taken away - we will see tomorrow how much effect that will really have.
"But on the other side it's going to swing towards us on Sunday in the race. We will gain a lot of time in the race."
Six-time world champion Hamilton, who set the Friday pace in a Mercedes one-two, said: "It affects qualifying a little bit but not massively. It does change things for the race.
"You should be in a stronger mode for a lot longer so it should be a faster race. But reliability is not given so maybe it'll push people reliability-wise, so we've got to keep working on it."
Indeed, the fact the impact the FIA technical directive could have on the reliability of engines over the race distance has been flagged by more than one driver.
"It's going to be very interesting to see how other people handle that through the race," said Racing Point's Sergio Perez.
"You may be able to see a couple of engine blows on Sunday. I think engines can be pushed to their maximum so it will be very interesting as you can only use one engine mode."
McLaren boss Andreas Seidl said they were intrigued to find out the results of the change on track.
"I think to a certain degree each team is having, or was having a kind of qualifying mode and the race mode but we don't know how big is this gap between and for each engine manufacturer," he said.
"We're interested in how it will pan out and also what the race power is for each team. We will find out on Sunday."
What are other people saying?
Carlos Sainz, McLaren: "Renault and us had quite a strong qualy mode which makes us look very good sometimes in qualifying. So I think it's going to affect us."
Max Verstappen, Red Bull: "For me it's not a bad thing. I don't think Mercedes will suddenly be a lot slower. We won't lose so much, they probably lose a little bit more, but they have still have such an advantage in qualifying that it will be enough for them anyway to stay ahead."
Lando Norris, McLaren: "In qualifying it will make it more even, 100 per cent."
Karun Chandhok, Sky F1: "Unfortunately, I can't see the pecking order changing. Everyone has got slightly different modes they have got for qualifying and the difference we are talking about is a tenth or two tenths.
Mattia Binotto, Ferrari: "The Technical Directive has certainly affected all power unit manufacturers but maybe not all of them in the same entity. For what is Monza-related, I think what will be used here is not too far to what we're already using in the past in the quali and that will be for the entire race distance, obviously."