It is possible, if you're willing to have whatever type of pet you've actually tamed appear as a gnome throughout the rest of the game. For example, if you tame a tiger, then every cat model in the game would look like a gnome. (Imagine gnomes wandering around Stranglethorn Vale, Teldrassil, etc. :P) I'm not sure how DBC editing works, because I've never tried it, but that's how it would work using a regular model swap.