I've heard a few songs (off the top of my head, A Dios Le Pido) where they pronounce "y" both with a y-sound and an English j-sound at times. In some songs, the different pronunciations occur when repeating the same phrase (from the song above, "yo a Dios le pido").
Is it just something that can occur in music? To my knowledge, people add accents in English music, but for any one song they stick with one accent. Is this not the case in Spanish?