Doesn't a manager or coach have to go to the umpire before the mound in order to make a double switch? Or is this just a myth? I have always heard it explained this way.

Last night in the Astros/Cardinals game, Jimy Williams went directly to the mound for a conference. When the umpire came to break up the conference, they had a long conversaion and Williams made a double switch.

This is OBR of course.

And he probably got his relief pitcher 8 more warmup pitches before entering the game.