WoW Model Viewer can be downloaded from wowmodelviewer.org. It is good to know that model viewer loads items and models from WoW's program files, so you can't run this program and the game at the same time.
You can also load a blank character using the File List on the left side of the screen. Expand the 'Character' menu, then pick your race and gender. This template can be customized using the controls on the right. You can change skin color, hair style and color, and facial features.
To change the shoulder back to the correct color, you're going to use the Animation box at the bottom of the screen. The second drop-down menu has all the 'skins' listed that belong to your shoulder model. This one only has 4, but some models have 20 or 30 skins. I just click through them until the one I want shows up on my character. After that, you can go back to the model control box, and repeat the process with the right shoulder.
Here's Draynee with both shoulders and sword sized-down. Once you have all your gear looking the way you want, you can play around the character's animations. First, go back to your model control box and pick the first model, in this case DraeneiFemale.m2. Then, go back to the animation control screen at the bottom, and have fun!
This is the first tutorial I've ever written, so if you have any questions, let me know!