Is there any way to programatically remap the keys in a Macbook running OSX Mavericks?
Have you looked into Keyboard Maestro?  I use it all the time,  I believe you can accomplish with what you want using Keyboard Maestro.

For example:  You can have it check for a typed in string "good" and return morning or afternoon based on the time of day.



With Keyboard Maestro you can execute AppleScript or Shell scripts.  Keyboard Maestro is pretty powerful.   Your macros can then be global or specific to an application.