We swapped Shimano brakes for someone Monday evening - basic 2 pot SLX units for 4 pot DeoreXT, as well as the levers. Just unscrewed the old calipers and fitted the new ones. Did the same with the levers.
However - it depends on the year/model as some have the slip-in fit and some the banjo fitting. If doing like for like it is easy and just requiores a quick bleed to finish up.
You can buy the banjo fittings & inserts that screw onto the end of the pipes (after removing the olive/insert and screw of the old type). Not sure where from, but my mate has just done this