Yep, looks like louvers to me too. It might fly as long as the plate was readable in the dark. It's a pretty neat idea.
I am 99% sure that it is illegal to modify a license plate at all in CA. I did the cutel little fog the paint from yellow to orange that so many used to on the old blue and yellow plates and was pulled over for that once and sited. I used the excuse that the plates were faded. Cop said I had to leave them as is or get new plates unless I could remove the paint. Overall I think it would depend on the cop and mostly the car. On an old Hot Rod or cl***ic I am sure they would turn a blind eye. On a primered 81 Monte Carlo, you would get a ticket. Btw, I think it looks cool.