You can change your line-up (even after participation) at any time until the end of a matchday. Caution: However, if you join during a matchday and players from your line-up are already playing, they will only start collecting points from the moment you join the Pitch. Points collected before that time will not be taken into account. Also, you cannot substitute players whose club has already started to play. (You can find the requirements for this here: Rules of the game).
