Special Thanks to Hans Palm
Mesh based normal map decals are only half-implemented in Unreal Engine (Unity engine is unknown). Conceptually it resembles using Trim Sheets. However, the difference is that instead of breaking up your mesh to following the trim sheet, instead you break up a decal planar mesh to follow the decals trim sheet, and overlay that on-top of your original model. For extra spiciness, you could do both.
Sometimes you will be able to design a feature using just NDO/DDO/Photoshop/Substance, other times you will want to bake the feature down from a high poly such as below:
*Note: By using a color ID map on your low-poly mesh, you can set-up your master material to apply different parameters such as tinting, roughness, and metallic parameters based on that ID map in conjunction with your other trim sheets and decals.
