I don't know about a script to do this specifically, but I wrote everything in LESS instead of direct CSS. This way you can put things like gradients into mixins (similar functions), and then you only need to change one small set of declarations. instead of doing this on multiple files. Of course, mixins generally result in a lot of reuse, not jsut for supplier announcements, but for many things (for example, I usually define a color palette and icon sets, as well as mesh mixins based on 960.gs).
On dynamic sites, I usually set things to compile on the server side and in the cache. On static sites, I just use a shell script to compile less css just before deployment.
prodigitalson
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