Hm, yeah this is pretty hard to solve since it needs to be on a dome and modular.
Given your strict requirement, I think you might have the most luck using a Light Function Atlas. This is a more expensive option than decals, but I think it will be the only solution that gives you a decent version of the desired effect.
You can read up on light function atlases and how to use them here.
Just make sure to enable “Translucent Uses Light Function Atlas” in your project settings and set your glass material Lighting Mode to “Surface ForwardShading” in order for the light functions to appear on your glass.
Here’s the test I ran on my end with it. Setting the Light Falloff Exponent lower, setting the Specular Scale to 0, and adjusting the attenuation radius helped focus the light too.
