i've known people that thought there was no such thing as "Christian rock" or that "Christian rock" was all of very poor quality, or that unless it was pipe organs, harps and choirs, it couldn't be "worship music" -- but changed their minds after being exposed to examples of very skillfully played Christian rock, or worship music in an uncommon musical style. for the most part it was just ignorance about what actually exists, not headstrong judgementalism.
as for myself, i've never put that sort of limit on God in my own mind. even before i started listening to, and actively searching for Christian music especially in the most obscure genres, i never thought it was "of the devil" or even that it didn't exist, i just had no idea that it did, and had never given it thought.
that's not *quite* what the OP's asking, but i hope close. i haven't personally ever seen someone who adamantly condemned all rock/metal music as Satanic change their minds about it. what i've seen is that even when you give them wonderful examples that contradict their thinking, they are blinded in their minds and refuse to even give it thought. they will say even though a metal band is singing a Psalm of David, because it is an heavy metal style, it is of the Devil.
this post implies a good point; it is probably a waste of time to try to argue with such a person.