You do not need to disassemble the recoil to change the rope out. That is why they put the small notch is in the Outside Diameter of the inboard side of the sheave, 180 degrees from the knot pocket. FWIW
You have two options:
If the rope has broken / unintentional retract? Remove the silicone plug around the knot. Remove old rope. Insert new rope, turn the rope sheave CCW until the rope can be put in the notch, continue CCW another 6-10 turns (until the spring tension feels right). Hold the sheave to the housing while putting the other end of the rope thru the housing grommet. Remove the slack and let the spring rewind the rope. Verify spring tension is adequate to hold a full sheave of rope and functions correctly. If you need more or less spring force use the notch and adjust it. Repour the silicone / RTV plug if desired.
If rope has not broken? Remove the silicone plug around the knot. Pull the rope all the way out (like you were pulling to start the engine). Hold Sheave to housing to not lose spring tension. Remove old rope (grab the knot and pull out backwards). Insert new rope (likely easier to tie the knot in one end, thread other end thru knot pocket in sheave and out thru the housing grommet) and let the spring do it's job . Verify spring tension is adequate to hold a full sheave of rope and functions correctly. Repour the silicone / RTV plug if desired.
Optional; If you want a little insurance to an unintentional retract and the exposed rope path is clear of obstructions, you can tie another low stress knot (like a figure 8) between the handle and the recoil housing.