I've looked in to this. The parts are availabe, but there is no "kit" you have to buy the parts individually, they are a little pricey, but not bad considering they are OEM parts from ford. From the looks of it, all that needs to be done is swap out the rear drum hardware for the rear disc hardware. And it all needs changed.. none of the drum components can be reused on the disc setup as far as I can tell, even the rear hubs/bearing assy is different. As far as the hydraulics part, just need to change out the rubber hoses from the main rear steel lines to the calipers. Master cylinders are the same, and the proportioning is done electronically with the ABS/ETC/ESC system. I priced the cost of buying the parts from ford a while back and its about a 700 dollar conversion estimate for the hardware.
I plan on doing this either next year or the year after as my budget permits.. I wanted to do it this year.. but, I ran outta funds for playing this year... (too many ideas, not enough cash or time)... but as a benefit, the aftermarket replacement guys will have a chance to offer lower cost parts hopefully by the time i get around to doing the conversion on mine.
As far as warranty? If someone is willing to actually tear the thing apart themselves and install the parts to start with, warranty shouldn't be an issue, because the new parts will carry their own warranty (often a lifetime one if you spend the extra for the premium version of the part) if something should happen to be made wrong.. and if something "brakes", we'll just jack it up, tear it apart and fix it..