There is a kiosk demo version for DK: King of Swing which exists. It is different than the retail version of the game. Only the first world is accessible by normal means in the demo version. There aren't much differences otherwise, but one could look further (like me comparing the two games). For obvious reasons, I won't share a link to the ROM. You're on your own there.
Visual Boy Advance codes
I happened to find these back in August 2013:
*02027a80:xx - Always enter mode
*00 = Cranky's Lectures
*01 = Adventure
03003eb0:xx - Always access a level
*00 = Banana Bungalow
*01 = Tropical Treetops
*02 = Contraption Cave
*03 = Puzzling Pyramid
*04 = Congazuma
*05 = Fire Necky
*06 = Explore outside of World One (turn off to access levels)
0300002c:99 - Infinite health
Differences
*There are two nearly-identical title screens. One doesn't have the copyright information on it, while the other one does.
*The credits instantly cut off when the second Special Thanks is listed, meaning that the ending wasn't finished yet.
*Only the first world is accessible, as I mentioned. I think it's called Jungle World.
*Cranky's Lectures is one of the two modes.
*The only two modes are Adventure and Cranky's Lectures.
Screenshots
Video of Credits: