I am afraid we don't have any compiler nor decompiler for the Nightfire model files, at the moment. I heard somebody is working on such program, though, it is unclear wether this 'rumour' is true or not.
If you want to change anything about the Nightfire models you can:
- change the texture files (pictures) in models/textures;
- open the models in a text editor, there is not much visible text but you can change the texture files a model uses, I think
- delete model A, copy model B and rename it to model A to have the model B used at parts which utilise model A;