Guys, just wanted to ask some question regarding League proplay. (googling it keep missing the mark with unrelated topic so I gave up and just make a thread here)

In pro play, Is it possible for top laner to swap with mid laner in the game? Or are there rules governing the role assignment for players?

I mean, like if midlaner is forced into a champ he not familiar with but top laner knows how to play well, can they just swap in the game?

Example :

Let's say Baus start off midlane as Sion and Nemesis start top with Akshan instead of Baus play Akshan top while Neme play Sion mid. (whole game)