I have only done it a few times.
It is a very strange operation to drop in a hive into the registry and edit it, using the quick method, but it worked.
You select HKLM in your current registry, and then the File/Load Hive operation will become usable.
File means you have to find the registry hive file itself by browsing.
Load in and name this "other" hive section which will look like it has become part of your current registry. Use a really obvious and different name, so you can find it.
The strange thing was why I would want to view this all mixed into my current registry, but thats what they said to do ?? There must be a better way to clear the slate and load in ONLY the one hive I want to edit, but it worked, so I rolled with it. I had a full backup, so that helped when presented with this odd method.
Whatever you do certannly do not Import it in, that would be a mess.
Make your changes, which should change it immediatly, Then unload the hive File/Unload Hive and then close. Selecting unload hive unloads the one you loaded (there are no options then).
more info http://technet.microsoft.com/en-us/library/cc732157.aspx although a good tutorial with pictures is what I used the first time.