John,

You can't retune reeds to be in a different key - you will have to replace them.

On most Cajun style accordions, that would be difficult because the reed blocks are permanently attached. It might be possible to remove the individual reeds and put on new ones, but the problem is that reed blocks are sized for the key of the reeds being used. Higher pitched reeds are shorter than lower pitched reeds, so things might not fit properly.

But the good news for you is that reed blocks on a Gabby Cajun King are removable/replaceable. You can open up the accordion, undo a few screws, pop out the old reed blocks and pop in the new ones. Easy peasy. You can buy the replacement blocks from Gabbanelli - they might even take the old ones back in trade, or you might be able to sell them to someone else.

-David