And another one!
A shader for mixing or blending together normal maps as outlined on this page:
(Colin Barré-Brisebois, Stephen Hill)
This gives much better results than simply blending or overlaying two normal maps. It uses Reoriented Normal Mapping as described in the article as well as the idea from the second comment, by “jarkko” in that article, which I have named Displacement Vector Normal Blending here just to give it a name. The modes are fairly similar in results.
Right-click and save both in the same folder, both are needed for the shader to work. Overwrite rhfunctions.h if asked.