You could pull off a PBR shader in 3D Rad with enough patience. You could have the shader read from a set of textures in the skinmesh's folder. But it's user unintuitive. 3D Rad is just not designed for PBR shaders. They are relatively "new" to the public user base, keeping in mind that 3D Rad is deprecated since 2012 (8 years now).
not possible, since PBR usually uses: occlusion/height/rough maps etc, and support for loading/rendering of those maps needs to be hard coded into 3drad's engine itself - not by user HLSL scripts. 3drad only supports spec/light/fresnel/reflection/normal/glow/RGB/alpha maps.
the best you can achieve is to convert existing shaders that use said maps, such as nvidia's ddGodRays shader that is sourced from an alpha map [unlike 3drad's cam sourced godrays] http://developer.download.nvidia.com/shaderlibrary/webpages/hlsl_shaders.html i started working on just that, and may try to finish it one day, but it's harder than i thought, you have to rename/rearrange the code to suit 3drad's custom built in functions, who's documentation is very limited or lost forever... also, there was an attempt by gene transfer to make a 'fake' thickness map shader so i suggest to look at that. since some of his and shadmars were based on xbox or nvidia shaders it's the best way to learn by comparing 3drad code changes from original.
you may want too look at nvidia's Relief_Mapping shader linked above. it does Parallax Mapping and Relief Mapping with Shadows using a normal map. as seen in the examples images i attached, this is pretty close to PBR but without roughness, which could be faked using a spec map for metal, etc.
let us know if you have any luck, even if you don't want to share your code just knowing it can be done is a great help.