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After you cook, you'll notice that your map has cooked to a directory like UDKGame\CookedSDK\AOCSDKLevels_E1ED54B24E9F8DE8C917B1ABC51E4040<GUID GOES HERE>. The bolded component there is the mod package's UIDGUID. You'll want to save this UIDGUID. In the future, when you want to recook this same map/mod package, you should add the guid to your cook command.
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Replace the "xxx" with the GUID of from your new package directory. Now, when you cook again it'll replace the files in that directory instead of just creating a new one. This is very important if you want to use the Workshop since it lets you just update your existing item.
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