Below is a very quick recording I made using my Hammond organ (XK-3c, not the M2 shown in the photo) 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, but on some verses there was no playing as I adjusted the tuning.

You can see that your hearing adjusts pretty quick to the new tuning. 

I was playing lead mostly, but the difference can be more dramatic when comping with chords and using pads on digital keyboards.

Through experimentation, you can get some interesting effects. Pro keyboardist and producers use this technique to bring something different to the table.

If only melodicas came with a quick tuning knob!

Lowboy 

Hammond Organ Tuning (430 to 450) Played with Song .WAV

Lowboy Bootay