Hi everyone.
The unimesh workaround does work now! I don't know why it didn't yesterday.
@Defaultguy. I didn't know you and Nerd3D are from the development team. Thank you for your quick investigation and feedback.

@ Y-Phil. That script will be very handy. Do you think it's also possible to enable all the "light emitter" checkboxes of multiple model's body-parts in a scene with a script?
I've never given Python scripts much attention unfortunately.