uneeq: I do not know if your first point is true that “If I was to change a music file in any way, by manipulating the bits that compose the song, I technically haven’t stolen anything. So simply by converting to MP3 format to store on iTunes I would be complying with copyright laws” nor am I convinced that it is relevant Hilchos Gezeila. Regardless, most people are copying music as-is, so your Limud Zechus is irrelevant.
Regarding your second point, Gezel is taking someone else’s property without permission. Even if the value of the theft is less thana Peruta, the Issur is still d’Oraisa. Anyways, it’s not my Chiddush. As I cited previously, Reb Moshe, Rav Elyashiv, Rav Vozner and Minchas Yitzchok all forbade copying tapes based on this logic. Your issue is with them, not with me.