It is easy to change the pull cord. Undo the four screws holding the drive shaft etc......This exposes the centrifugal clutch assy. In the end of the clutch assy is an allen srew, undo this. To prevent the crankshaft from rotating insert a small screwdriver into the hole provided in the crankcase. Unscrew the centrifugal weight unit. Now you can remove the cover holding the recoil start mechanism. From here all is straight forward.
Tony King, S W France, May 2010