To play with it a bit there are variations on a theme (sometimes called "noodling", and sometimes "ricercare"). If one uses the hard "C" of the Latin one could say that a "ricercare" was an expression of fandom for Ricky - whether the late Nelson or one of the moderns. But taking the tongue out of the cheek I might ask if you could suggest some other examples - variations (as used in titles) doesn't fit. But I think one might find a number of examples in Bach, or in any player who works within the music but plays off it. Perhaps classic Jazz, with the play off a pattern, would fit the definition. I've always thought Bach might have enjoyed Jazz improvisations.
Best, Jon
