Not sure exactly what the point of changing to discs would be. Electronic brake force distribution does a good job of balancing the brakes individually as it is. I have discs on mine, but that just means higher operating costs and brake dust on the rear rims. The point about nose dive doesn't really make any sense because braking with the rear wheels exclusively still causes this effect... not that the discs are going to grab any harder than the drums.
If you are going to do it, I certainly can't imagine it being cost effective (probably would have been better just to order one with them if they mean that much to you). Best be careful all the sensors for ABS and EBFD are sorted out, and there could even be insurance or inspection issues that would arise, so it might be worth an investigation on that front.
Originally Posted by Focus YBTC
Why would the warranty be affected? If you use Ford OEM parts the worst that could happen is they wouldn't warranty the disc brakes themselves but the brakes would have their own warranty from buying them as genuine Ford parts.
The difference is that those genuine parts weren't for your car... they don't tend to warranty modifications like that.