Depends on your own circumstances, some people see an increase in price, some only have to pay an admin fee. I know you could buy them directly from ford, I can't remember if they were offered from the factory though, I think regardless the fact that you've done it now its an aftermarket modification.
On a related note, I've had bilstein b8's fitted today, and the car feels a lot better now, found another blown cv boot though, and the handbrake cable is seized, ahhh well, lol. Also oil filter diaphragm housing blew its top a few weeks back as well but that got sorted pretty quickly.