There is a lip all around the lense that has to be very carefully ground off with a Dremel etc.
I started to experiment with this on some spare lights. You would then have to bond the lights back in...i've not got to that stage yet, not high on my priorities at the moment. Be warned, you may find that the lenses don't quite fit afterwards. When manufactured, the lenses appear to be inserted with a process using heat, this makes the lenses a very tight fit in the aperture. The new chrome will make the aperture just that little bit smaller, and the lenses don't quite fit. Ask me how i know! Also, i am not convinced about the bonding either, both onto chrome and you may have a slight shadow all around the lense.
I machine polished the lenses too.
JP