Would it be possible? No, not without the game's main source code, which we currrently do not posess. Would it be a good idea? Possibly, though adding an entirely new model would require a lot of coding, new textures, markings, and actions.
Sadly, even if it was possible to add a new model, our game creator, KovuLKD probably would decide against it, since the feline-canine theme is really all that the game was meant for. There will be many new models in the upcoming game Aro'kai however, which you can find out more about on your own time ^^