Hi Steve and All,
Below is a link to a quick recording I made using my Hammond organ (XK-3c) and adjusting the tuning between 440, 430, and 450. The organ is played to the same backing track as my last melodica comparison.
Verse 1 = 440
Verse 2 = 450
Verse 3 = 430
Verse 4 = 450
Verse 5 = 440
You can hear me slide the tuning up and down on a couple of the verses. On some verses there is no playing as i adjust the tuning.
You can see that your hearing adjusts pretty quick to the new tuning. Going from 450 to 430 and playing down low gave the most weirdness until I started playing the upper register.
I was playing lead mostly, but the difference can be more dramatic when comping with chords. Through experimentation, you can get some interesting effects. Keyboardist and producers use this technique to bring something different to the table.
If only melodicas came with a quick tuning knob!