The V-Ray Decal provides an easy way to project one material on top of another, regardless of the target UV set. The projected material is placed in an adjustable V-Ray Decal gizmo that controls its size, placement, and projection limits in the Viewport.
Multiple V-Ray Decals can be stacked on top of each other, and their overlapping is controlled by the parameters in each V-Ray Decal object or by their positions in the scene.
Example video from the V-Ray for 3Ds Max integration:
https://www.youtube.com/watch?v=lzQ4g3_9VIA
Submitted on AHA Ideas (VBLENDER-I-18).