Not sure why this isn't out yet, but there needs to be a way to officially trade roles with someone in champ select, like the trade champions button. This will change the role under the summoner name to what they're going to play. It would avoid confusion in champ select from people just saying in chat what role they are.
Now that I think about it more, this could make catching people who don't go their role a whole lot easier, if you were to report someone for such a thing. It would also make a definitive answer for if you ask someone to swap roles and they don't say anything until late.