Libreto literally translates to "script" or "libretto" (as in an opera). It's a word that evokes a sense of pre-written destiny or a planned sequence of events.
In the song, Daddy Yankee sings, "Te diré mi secreto, cambiaré el libreto" (I'll tell you my secret, I'll change the script). He uses it metaphorically to express his desire to break from the current, platonic storyline and rewrite their relationship into a romantic one, making it a compelling and unique choice.
Have you ever fallen hard for a friend and suffered in silence? That exact agony drives "Si Supieras" by Puerto Rican reggaeton heavyweights Daddy Yankee, Wisin, and Yandel. The title means "If you only knew," and the whole track is a confession of feelings kept quiet for too long. Yankee admits that his hands literally shake whenever she is nearby ("Que me tiemblan las manos cuando la tengo cerca"), calling it pure punishment that she has no clue ("Y para mí es un castigo / Ver que no se de cuenta"). He tries to fight his own thoughts to forget her, but her face, hair, and eyes completely break his willpower.
Wisin jumps in with his signature direct style to speed things up. He drops the polite act, saying "no quiero ser más tu amigo" (I don't want to be your friend anymore) and tells her to sit down and listen. He drops fun, cocky metaphors, calling her "de caramelo" (sweet like candy) and describing himself as a shark waiting for her to take the bait ("El tiburón esperando que muerdas el anzuelo"). He even refers to himself as "el tigre W" (the tiger W) ready to fulfill her fantasies. It is catchy, smooth, and full of great everyday phrases for expressing pure infatuation.