Yes you can! The Focus SVT model comes with rear disk brakes from the factory and the parts from it will work. There's also a kit from Ford Racing that has all the parts needed to make the conversion. It a fairly straightforward swap and can be done in an afternoon. Look on EBay, they have thousands of part for the Ford Focus, including the disk brake kit.
My friend is having the same problem with her 2011 Focus. They told her it was to do with the traction control kicking in. She said it occurred out of the blue and wasn't under extreme conditions or bad driving. Ford replicated the locking and traction control activation during a test, but they said it wasn't a steering or break issue.
To adjust the rear brakes on the 2001 Ford Focus ZX3, first remember these brakes are self-adjusting. Drive the vehicle in reverse and press the brake a few times to clear the lines and set the calipers. Then, stop the car. Place it in park and pull the emergency brake. Pump the brake while the vehicle is turned off. You will feel the brake peddle stiffen.