You are right Kurgan, it really only works well for saber duels, which is what I use it for. I guess I didn't specify that in my last post
As for using downloaded skins/models in single player, you don't have to edit the assets0.pk3. You can use the same mechanism that you use to add skins to MP. What I did was extract the pk3 file, and change the directory name to the SP NPC you want to replace. For example, if you want to replace the reborn with Maul, you would change:
models/players/maul to models/players/reborn
Once you do that, go into the directory with all the model and texture files, and you will see a .skin file. Open it up and you'll see a bunch of file paths. Replace all "maul"'s to "reborn". Then put everything back into the pk3 file, and put that into your base directory. When the game loads, it will also load this new .pk3 file and replace the models from the original game.
This technique is the same as the one to replace kyle with a different skin or model. I think there are a few threads on this forum (might even be a sticky) that discribe this process in more detail. The only difference is that you don't change the directory to "kyle", but to whatever NPC you are replacing.
Hope that helps