Is it possible to fix or patch this add on and play it without the full version of Call of duty installed?
Welcome mcalcagno698 :),
you have to install COD and COD add on to play. If you like to play it without CD you can create an image of your original using your favorite burning software which is able the read SafeDisc and mount it using Daemon Tools.
would this be illegal, to play the expansion pack without owning the orignal game?
Its impossible dudes. CoD UO uses parts that are orginally in CoD, otherwise my image (Alcohol 120% made :P) file would not be around 500mb. Otherwise it would be around 3cds.