If you want a new background but don't have a clue about how to uvmap the background model, just replace the textures using modelview and save with a different name. It's a 2 minutes job, no need to have coders doing it, and surely if it has to be done, don't scratch the actual system.
most background images do need some uv work, you may want to use more than one, you may want a different uvscaling to have the same background image looking like if it is more far or closer in different missions, or you may have an image on top instead of on the left, etc etc.
Not always the background textures are interchangble, and specific pof models give to modders higher power in adapting the thing for their specific needs.