Custom attenuation can be done with a light function by getting the distance between the pixel position and the light position (for point/spotlights). Unfortunately you can’t get the light position from the material editor which means you’ll need to make it a parameter and set it from Blueprint.
In your light, you’ll need to disable inverse square falloff and set your falloff exponent as low as you can get it (since you’re effectively overriding the attenuation yourself)
For what you described though, my advice would be to just disable inverse square falloff, and use the exponent and the light intensity so that you dont have such a bright hotspot. I don’t think you really need a custom attenuation curve.