Let's clarify some points about the french rosters :
1) In my case, I was already in FRA but was swapped with Vade, someone which actually never played an official match, which regarding the rules doesn't even count as a roster change. This leaves us with Drake, SharZ and Obelix.
2) When lebrave posted the french roster change before the semi-final, all the guys mentionned as "in vacations" were indeed away :
so that it was necessary to make this roster change in order to actually get enough players to for the match, not knowing when exactly the others would come back etc (some not wanting to play aswell, like tiberias for example).
And this was the fse post mentionning the final roster change which was accepted by the organiser :
3) Besides, Drake and sharz were already in the original roster when the french team signed up and played its first matches, and were indeed exchanged with players which maybe showed up in the beginning (tbh I don't remember seeing them a lot, like Bastille, Diablo, Tytygus etc) which makes them legitimitate players in the french lineup which again was agreed by the organiser, leaving Obelix the only new face (and not a known one) in today's lineup.