It's like that meme where it's the guy saying he just needs that one piece, and the piece is labeled "a billion dollars"
I'd say it depends on the length of the dialogue. If we're talking about 2-3 lines, then yeah, it should only be done on switching. If we're talking about a speech that lasts several pages, I would think that it should be clear from context clues who is speaking.
Anyway, don't get hung up on rules! Write how you want! Have a style!
Looks cool, best of luck.