How do jazz and rock arrangers change melodies and harmonies while keeping a song recognizable?

In the context of musical composition, jazz and rock arrangers maintain the recognizability of a song while exercising creative freedom by balancing structural preservation with stylistic embellishment.1

Rather than merely transcribing a piece, these arrangers often act as improvisers on manuscript paper. They manipulate the original material by:1

• Melodic Embellishment: Arrangers and performers frequently decorate the melody with ornaments, figures, or motives, ensuring the core identity of the tune remains intact while adding personal expression.12
• Harmonic Expansion: They may elaborate on the original harmonic structure, providing new textures or "filler" that supports the melody while offering a fresh sound.1
• Instrumentation and Scoring: By assigning specific roles to different instruments—such as having saxophones carry the melody while trumpets provide counter-melodic figures—arrangers recontextualize the song for their specific ensemble.1

Ultimately, the arranger’s skill lies in their ability to transform the composition through these variations while retaining enough of the original material for the listener to identify the source. This practice reflects a broader tradition of musical variation, where the goal is to provide contrast and originality without losing the essence of the work.13