The first two digits of form IDs found in add-ons are given as xx, because they may vary depending on the number of active add-ons and the load order of them. Objects from a specific add-on will all have the same two leading digits. If Dawnguard is the only add-on you have, the xx for the IDs should be replaced with 02. In most cases, to find out the first two digits for an add-on, activate the console and click on an object from that add-on to get its ID or use the help command with an add-on specific text. The Nexus Mod Manager also lists the correct ID.