A question I often get asked by my students is how to go about reharmonizing a tune. This is a brief video outlining some methods I use. Jump to https://youtu.be/4CfqXH-hpQE?t=555 to hear my improv on the reharm. It is assumed that you are already familiar with jazz chord voicings, extensions/alterations & substitutions. If you want to follow the chords that I’m playing you can download a PDF of the lead sheet here.
Jazz reharmonization is a vast and beautiful area in which I continually encounter new insights and surprises. There are many books available on this subject, and transcribing reharmonized tunes by jazz greats will not only improve your ear, but give you a first hand look at how they approach improvisation on the new chord changes as well.
P.S. A minor slip of the tongue at 3’42” – the chord is a Gm9sus (not G9sus) and at 4’55” C#dim not C dim.