You can't change an already recorded piece that uses A below middle C at 440 Hz, to be tuned to 432 Hz.*
I'm currently designing software synthesizers, and they can be tuned to A432 (or just about anything else). Unless you have perfect pitch you'll never know the difference. It's pure snake oil.
What I do find interesting, and am able to hear is other temperaments than "Equal". The one that I like the most is the rediscovered Temperament designed by Bach.
http://www.larips.com/ The reason this can be heard easily is it changes how the notes of a chord "beat" against each other. Even without perfect pitch, having a lifetime of listening to Equal Tempered Western music, when you hear something that's tempered differently will strike your ears. With Equal Temperament key doesn't matter, it's just putting your hand in a different place on the keyboard, but the spaces between notes are exactly the same no matter where you start. When you change the spacing interesting things happen, and different keys take on different characters.
But changing the temperament of a synth is much more difficult than scaling everything to be based off a new A frequency. Each key in the octave has to be retuned, this is each enough with pianos and their family, but impractical or impossible with other instruments.
*I supposed you could slow down a song very slightly, but yeah, it doesn't make a difference.
