Judging from these two pictures, it looks like the class reassignments are minimal, most of these students are consistent.
The only information offered is that Chloe has been consistently allocated to Marinette's class.
Although, knowing Chloe, I wouldn't be surprised if that was intentional, that's she's pulling strings to make sure it happens, just to keep Marinette nearby to torment.
The reason I am mentioning it is because it was suggested that Aurore and Mirielle could be assigned to Marinette's class in order to give them more character development.
But which two characters would be transferred to Ms Mendeliev's class in that scenario to make room for these girls?
Or would they just add them to the existing class without swapping students?
Given that Marinette didn't know whether Chloé would be in her class, it seems that some swapping definitely happens.
Here are my rankings for who I think is likely to be swapped out, from most to least likely:
Ivan and/or Mylène. Their character arcs feel pretty much complete, and it doesn't seem to me like either the fans or the showrunners have much admiration for them.
Kim, Max, and/or Alix. I'd be sad to see them go, but their dynamics were (unfortunately) such a small part of the first season that their absence would be relatively unnoticed.
Nathaniel. He's a fan favorite, but Thomas Astruc stated he had never expected him to be so popular, so there might not be plans in store for him.
Juleka and/or Rose. This would be a surprising change, given Juleka and Rose's increased prominence in the recent webisodes, but I think this would be more likely than anything later on the list.
Alya, Nino, and/or Sabrina. I wouldn't expect the showrunners to separate Marinette, Adrien, or Chloé from their closest friend/underling, but it could be good for character development.
Marinette, Adrien, and/or Chloé. If Marinette ended up separated from either her crush or her nemesis, I'd be very surprised—and I'd applaud the showrunners for taking that risk.
So my guess? I'd cut it off halfway through the second row—I think the new class will have Marinette, Adrien, Chloé, Alya, Nino, Sabrina, Juleka, Rose, Nathaniel, and either Alix or both Kim and Max, but not all three.
Then there would be either three or four spots in the class for new students, one of whom would probably be Lila, leaving two or three spots for new students.