I would recommend using the Select Texture By ID method using the data editor:
http://www.sc2mapster.com/forums/resources/tutorials/20772-data-actor-events-message-texture-select-by-id/#posts
Import the new textures and follow the tutorial, but change the actor data for the new unit instead.
This way you do not need to create or duplicate new models.

Andrettin Regular ShmoeHow would I go about changing existing models so that they use a different texture?
I found these retextures of the Terran buildings and units to be quite interesting, but I want to use them alongside the normal Terran units and buildings, and in order to do so I need to create copies of the models with just a change in texture path.