Remixing in the popular music sense means the production of a derivative work from portions of the original plus other material.
I really like that when it's done as a cover of classical in another genre, for example a rock medley like A Last Illusion by Trans-Siberian Orchestra. If we're talking purely classical medleys/remixes, then that's neat too, even if I'd probably rather listen to the original pieces.
In the end, many composers did variations on themes of others, so why not!
