f2 can't change any session settings
If you start a career mode starting in f2 and choose no practice you will not be able to change any setting of every session (distance in the race or type of qualifying) also if you do qualy, 3 laps ...
Forum Discussion
For the difficulty yes, after quali you can change the difficulty if you close the game but for the distance you can't do much
Haven't got this year's game yet but I remember from previous installments that once you set up a season you can't change it until it ends, that includes sessions and their length.
