As you seem to be using OO (judging by the looks of the first parameter, with the name $self), why don't you just subclass SWMetal::Buffs? That's more sane than globally override a method, so that the original method no longer exists.
Comment on Re: Overloading subs = weirdness in mod_perl
That would be much better, true. But what I want is all calls from anywhere in the program to WSC::Image::list_images to be mapped to my custom subroutine (for this site). With my somewhat limited knowledge, I didn't think that subclassing would do that. Is there a way to make it work?