I'm not familiar with the Koyo rack but the basic job of changing the high pressure hose is not difficult if it is similar to the other brand racks. First compare the two hoses to determine correct length and type fittings at both ends. If the connecting point at the rack uses a "banjo" type fitting I would only warn that it is possible to overtighten such a fitting to the point of breaking it (it's a hollow tube after all). Use new copper washers (need not be from Volvo--a well equipped hardware store should have an assortment). The fit around the banjo bolt should be as close as possible. If none are available you can use a propane torch to anneal (re-arranges the molecules) the old ones.
Remove the lower splash shield and set a large enough pan underneath the car. Use a suction bulb to remove as much fluid from the pump as possible. Start at the lower fitting -- loosen and let the fluid drain. Move on to the pump connection when draining is done. Fit the new hose with the orientation of the banjo fitting same as the original.
When done fitting the new hose refill the pump reservoir and start the motor. Spin the steering wheel lock to lock--use even, slow motion. Back and forth - 5 to 10 times should be plenty to bleed out air. Recheck fluid level and road test. -- Dave