Maybe improvisation, perhaps re-arrangement or re-interpretaion.

My first thought is "travisty".

After that, I would say you would use the medium to describe it. Example would be, Hip-Hop Version of Bach's Cantata. Jazz version of Bach's Cantata.

If you are taking the whole piece and putting it into a new style, I would call that "Re-tooling" a piece of music, or for years we have used the term. "Re-setting".

I would call it rubbish. Peices arew written to be played in that style. I'm sure if pachable herd the rock version of canon in d or bach herd sky's toccata in d they would have a heart attack!

You could call it 'converting styles'

A travesty.