Custom Error Messages per promo code used

[Bruce - PhosphorMedia]

You'd have to monitor "l.settings:error" for the specific default message and global (CGI) variable of the specific coupon then display your customized message.

[Johnburgess]

I would like to deliver a custom invalid promo code message if a certain coupon code is applied. I can change the message that shows when a promo code doesn't work, but how can i target one specific code that being used?