Manipulate Data in the cache proxy server DB

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http://serverfault.com – I am wondering if it is possible to manipulate (Insert/Delete) data in the cache proxy server DB... well I'm not sure how a cache proxy server store the data. But What I am interested in is to add resources to the data base of my cache proxy before it gets it. An example for clarification purpose: say you have downloaded some web page before, and now you are installing a cache proxy server, and you want your server to use the downloaded data, is such a thing possible? discard the fact that it is a stupid way, or web pages can change during time, I would be thankful to know if doing such is e (HowTos)