Thank you.

Although materials may be set a-glow using formal 'emission' via 'nodes', super-dialling 'ambient' still works. Albeit with same limited, area-dependent surface brightness.

I'm sorry for posting different aspects of my complex query in different places, call it 'Exasperation Spill-over'.

Whatever, there's no 'quick fix' via hacking the MTL due that undocumented import 'trap', and nimbly navigating 'Material Room' is beset by UI issues.

So, must do it the hard way: Learn 'nodes' beyond rudiments, dissect the OBJ...

The former because essential in P12+, the latter as I did something similar with a RM RE2 scene, a big freebie found on SCG. Had to split out the multiple luminaires as a separate material when 'ambient masking' did not work. Poser 'group' tool proved too clunky, I resorted to CAD...

Again, thank you all.