According to the rules released by the FIA, after the practice sessions, only necessary fine-tuning on the car setup can be made, such as simple adjustments to the winglet angles.
If you want to change the engine power settings, you must get it done before the practice session ends, otherwise, it will be considered a violation and you'll be penalized with a grid drop.
This rule exists to enhance the viewership and unpredictability of the competition; otherwise, every team would prepare two sets of setups—one for top speed during the qualifying and another for the race.
Without the balance adjustment space, car performance would become the absolute ruler, and there would be no dark horses in qualifying and the race.
The root of the F1 history development and rule changes over so many years has always been about making the team strengths more equal, instead of the race outcome being a foregone conclusion before it even starts.
