I think AJ is the only one who messes with that stuff and could really change anything. But I think he's happy with the site's current Bully theme displayed for members. I know I am. Sites with customizable backgrounds remind me of....Myspace or something.
You might have to stick with just being able to customize your individual profile.
But who knows, the site has certainly gone through some theme updates throughout the years. So you never know what changes await us in the distant future.