Re: Rear Light...
It's pretty easy to do. Even the manual shows you how to do it (for replacing the bulbs).
There is a clip behind the bumper, on the underside of the light assembly. If you push it up the whole thing should slide out. This will not make it work like a reverse light. You need to change the wiring for that, but ford should do it (they say they will when they fit the factory body kit, so it has to be possible) or at least tell you how.
Cost wise, I think it was around $30-$40 dollars, but I checked that a while ago. If you don't change the wiring, be prepared for even more people to tell you that your drivers side reverse light is broken!
3-Door Focus Zetec manual, Machine Silver
Eibach Pro Kit, 2 1/4" Cat back exhaust, Tinted, K+N panel filter, Zetec mats
Leather/Aluminium Gear knob & handbrake cover, ST170 indicators