Title pretty much states the question.
I have several Triple and Quad builds that project Stars or lines from beam. On the Ledil Cute Triple the 3 Legs act as bright line artifacts on the outer beam shot. Also the XP-L HI spills more light inside the head, under the optic creating a starry effect.
Plastic friendly paints are out there. Just wondering it it has been done with good results.
I painted the back side of a Carclo 507 once—was thinking on the same lines you are—I didn’t like the results— it seemed like it cut the lumens/output way down—made it more like three individual lights— I usually use the frosted optic now and sand/polish some of the frost off then polish—for the quad optic I use a clear and sand it with 1500 to make it frosted
Plastic optics depend on the difference in refractive index between the plastic and the air surrounding them to create the reflective effect. Contamination in any form allows light to leak past reducing the mirror effect. Paint would ruin the reflective surface not by damaging the plastic but simply by being there.