"But why is there no obvious way to 'browse' for a strayed MTL within Poser ?? It would also be a real-neat, portable way of loading scene texture variants..."

And the same for FBX files, too many of which have hard-pathed texture calls into author's folder tree. Even 3D Paint has an option to navigate to texture directory. Where this falls down, of course, is when author segregates textures into several folders...

I'm currently trying not to perpetrate the same bloopers while exporting PP2 library files...