Is this the keyboard commands library written by Adrian Crenshaw? You didn't link to it or post the code?
As I recall, that library just called the normal keyboard functions, so it ought to work on either board.
Did you try compiling any of the library's examples? You don't need to have a Teensy to just download Arduino, install Teensyduino, select Teensy3 in Tools > Boards and Keyboard in Tools > USB Type, copy the library & load an example, then and click "Verify".