So I was thinking of making a hacked stage out of custom stage parts (I believe Mewtwo2000 did the same thing). But how do I do that?
Open STGEDIT_01.pac or whatever its called. there you will find all the models and textures for the custom stage. you can extract the models and textures, and import them where you like.
Also is it possible to make an .mdl0 file load a texture with a diffrent name then the original (as in putting down the same model in the same file twice but both load diffrent textures)?
Thanks in advance.

yes, press the plus on the model and go to textures1. there you will find a list of textures it loads. rename one to a name of a texture that you have in your texture data and it will be loaded instead of the original