Try using a clear coat like what's applied over the colour paint on cars.
Lightly dust the reflector with the spray rather than trying to totally coat it. I'd also go with less is more and allow to dry and test then re-coat if required.
I think you'll get a good result unless of course you mess it up.
The only example I can show currently is a mod I did many years ago and it's a bit different but essentially the same process. I was looking for an even projection of light which this achieved. Throws an even disk of light from centre to perimeter.
I used white paint and dusted the reflector with a total stippled coverage which might be hard to see in the picture. It's holding up great and works great.
Obviously you'll be applying much less paint, be using clear coat and obtaining a different beam type but you get the idea.
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