Technically, everything is code-able. However, this is code written by other people that Vekseid needs to get accustomed to before he can mess around with it, which could make things drastically complex.
Changing an image is really easy. Heck, he wouldn't even need to change the code, he could just replace the source image. Having signatures move from the first to the last post on each page is something entirely different.
I would actually like the signature only appearing once per post, and dislike scrolling signatures with a vengeance, were it not for the fact that the [ hr ] tag, which is awesome for splitting up posts makes the last part look like a signature.
Come to think of it, would it be possible to change the style of the signature line a bit? Like make it as hard as the line directly above your post, and below the "Reply #XX on: Whenever" text? That would differentiate the signature line from the [ hr ] line and prevent this confusion.