One more node group for your collection… 
This time to combine two Normal textures into one.
This was the best formula I could find.
Original papers here.
very nice, didn’t know that it is actually that complex^^
will definitely try it out when i need it.
Stan Pancakes made some small modifications to the node, so it has a mixing factor.
Check it here:
http://www.blenderartists.org/forum/showthread.php?349153-Baking-Normals-within-other-maps&p=2731572&viewfull=1#post2731572
Cool Stuff !!! :eyebrowlift2: