In football it is my assumption that any players on the same team can exchange their positions without waiting for the ball to leave play or without making any explicit indication to the other team.
I would like to know how this applies to the goalkeeper:
Can any player assume the role of goalkeeper?
Do they need to change clothing with the goalkeeper?
Do they need to announce this change to either the referee or the opposing team?
Do they need to wait for the ball to leave play?