Changing the root node name of your schema after extensive mapping can be a real hassle with the BizTalk mapper. The map editor will just drop all the links. To get around this edit the BTM file directly. Open the map file in notepad and simply go through and do a find/replace on the old root node name.
This can be handy when changing the fully qualified name of an external assembly too. Lets say you change the version on an assembly being used from a map. The BizTalk map editor will drop the assembly name from your scripting functoids. Just do a find/replace in the BTM file via notepad on the fully qualified assembly name.
Simple tip but it can save a lot of time!