Hi! This is a user-to-user forum. I recommend that you submit your feature request directly to Adobe using their official Feature Request and Bug Report Submission form:
For future reference, it is possible to change many of the keyboard shortcuts in Fireworks using the Keyboard Shortcuts dialog (under Fireworks > Keyboard Shortcuts). Here, you can choose from several different sets or create your own customized set. Within each set, there are three categories: Menu Commands, Tools, and Miscellaneous.
Unfortunately, none of these categories seems to include the shortcut to which you're referring (for text kerning). To expand upon your suggestion, I'd recommend that Adobe consider adding this missing shortcut to the Miscellaneous category, or create a new category called Text, where users can access and modify this and any other missing, text-oriented keyboard shortcuts.