OSL Shaders: NormalBlend.osl
NormalBlend.osl
This shader accepts 2 normal maps in linear space and blends them, preserving details.
The blend method currently installed is the reoriented blend method which is superior to most, if not all other methods.

2 normal maps blended. MixA = 1.0, MixB = 0.46, rendered with Arnold.
Download & Support
UI:
Supported Hosts: 3ds Max, Maya, Houdini, C4D.
Rachid Hadj Abderrahmane wrote ui files for Maya, Houdini & C4D.
Noodle:

Remember to set your textures gamma space to 1.0