I finally managed to solve the problem with the not consistent normals alignment in TextureVariation node 
I had to modify the blueprint of the TextureVariation_RotateUV Material Function used inside the TextureVariation node with the code from the link I posted ( this one ):
The new function rotates the UV of the same amount as the original one, but it uses Rotator nodes for it and a different pivot point. It also has a new TextureObject input for the normal map and a new output for the realigned normals.
The TextureVariation node was modified to support the new TextureVariation_RotateUV function, simply adding an input node for the TextureObject to feed the rotation function with and the nodes to manage the its output:
Lacking a background in texturing theory, to try to figure out how to make all things work as desired has been a very frustrating process! I don’t even know how much reliable or well-performing my solution can be, and I would also like to extend it with triplanar projection.
Also, I still have to find a way - if there’s one - to make dithering work!!! 
Any tip on the topic is welcome
I hope my experience can be useful to someone else! And feel free to leave comments to improve my material 