Well I had actually been doing 'differential' exports for the latest version. I would export once using "release" settings, and once using "all as full age" settings, and I would end up with different files in the texture cache.. Because when compressed the sky dome texture would noticable loose quality (overly smooth gradients don't compress too well) so I would put the non-compressed texture cache file put it in my regular export cache folder and then re-export to end with a textures PRP with all my textures dully compressed except for the sky textures..
A bit of a convoluted method when at first sight, but it worked. Reading Robert's previous posts I wonder if I had that method right or if it was sheer luck...
For the next version I will start using PRPexplorer, that should make things easier.
I took a look at the material panels and I can't see either any button we could use. That's in this kind of situation that I curse Blender's interface and its scripts integration.. It'd be so easy in any other 3D software to just add a PyPRP panel next to the regular Material panel and stick in there all the buttons and fields and checkboxes we need..