It all depends on the type of customization you want to do. I'm asumming just painting it a different color which is fairly simple if you don't mind the chance of destroying the casing if you're not careful. I've done this many times because I custom paint xbox 360 accesories...for a price of course.
I'll give you a free-bee though.
1) Start facing the bottom of the chat pad.
2) Remove the 4 torx screws. (two at the bottom, two beside the adapter at the top)
3) BEING VERY VERY CAREFUL, use a very small flat head screwdriver and pry the two halves of the casings apart at the top. There will be a pop as they seperate and this is normal, unless you see pieces start to fall off.
4) Once you have the two halves apart, disconnect the keyboard from the controller adapter. It'll be the only plug you see.
5) Remove the adapter from the bottom half by sliding the metal clips until they pop under the adapter posts.
6) Remove the 4 phillips tip screws holding the keyboard and push forward, again CAREFULLY. It will break.
After you've done all that just paint and put it back together by reversing these directions. The chatpad is surprisingly fragile. If you break the casing it will most likely still be functional, but look terrible. I've been doing this since the 360 was released and I still break many casings. If you still want to do it, that's all you need to know.
Hope it helped.