This int worth a how to do so I'll put it ere instead.
I bought some smoked headlights with snapped brackets (useless basically). I took my old head lights out (see removal of bumper in how to do - very very easy).
There is a thick black silicone glue that holds the lens on to the holder. I heated the glue with me girlfriends hair dryer.
Get a butter knife n start prizing the lens away from the back of the lamp. Be steady not to crack the lens. Be forceful but gentle as well.
After a bit of patience and you've been all the way around the lamp you can get the lamp in two hands and pull apart slowly. the glue goes all stringy, I found it best to cut the glue with a stanley as you pull it apart.
You will now see that there are three parts to the light.
A bulb holder (back),
A silver or black plastic interior
and then the lens.
Basically the GSI/SXI lights are just a black plastic interior in the light which gives a tinted effect.
With this in mind. rather than buying GSI lights, simply take your standard ones apart n spray the interior bit whatever colour you wish!
To put back together I cleaned everything (all the green moss builds up) and reversed what I did to take apart. The clips on the lens take a while to get in place because you should be pushing the lens back into the glue as securely as possible to make it as air tight as possible to stop any mist getting inside the lamp.
You could silicone the whole way round as well, but I didn't and mine seems fine. Good luck anyway.