Re: Change user in the Simcity Buildit

You can create 2 Game Center IDs/Apple IDs but you run the risk of a game being over written in Game Center. If you play another building type of IOS game that has Game Center linked games, one game can override the other (replace it.) I myself have never tried to use two different Game Center IDs/Apple IDs on one device because of the risk of one game overwriting the other's data but I heard about people who have.

You might want to research it more on the Apple help site before trying it. Seems a few people have had problems with it replacing one game for the other.

Your Game Center is linked through your Google account, as for your other question.