Short version: it's truly as easy as unbolting the old brakes and bolting the new ones on.

Long version: this bike came with integrated shifters and brake levers with the factory cable disc brakes. Converting to hydraulic, and ditching the brake levers, meant needing separate shifter pods as well. I wanted to upgrade to 9-speed anyway, so I was going to buy shifters in either case. Fortunately, the rear brake used full length cable housing (rather than cable stops with exposed cable), so I could run the hydraulic brake hose without any other modifications. You'll probably note that my rear hose is way too long (large loop up near the handlebar); I bought these brakes used from eBay, and I just haven't re-sized the rear hose yet. The front one is perfect, but I could take about three inches off the rear hose and tidy up the cockpit area. The front is a post mount on the fork and the rear is an IS mount with a 160mm rotor mount. Outside of the shifter pod change, I simply unbolted the factory Tektro calipers and bolted on the new-to-me Shimano hydraulic calipers.