It did occur to me as I was watching the video I linked that the Kagamine twins are young enough (and similar enough) in appearance that they could probably dress as each other and get away with it half the time. If I were writing their mascot profile, I'd note that at around age seven, they attempted a complicated scam that involved convincing someone that they were quadruplets: Rin put on boy's clothes and acted extra brash and cocky to generate an additional brother, and Len wore girl's clothes and acted solemn and demure when Rin's sister was needed.