I very recently watched 3 or 4 videos on replacing pull ropes. Every one of them pretensions the cord before attaching the pull handle.
WHY?
Please note the rounded grove on the edge of the take-up spool. If you completely install the cord (both ends no tension); then put the cord in that notch; turn the spool opposite the direction it should turn when pulled, it tensions the return spring and you don't have to fight the spring when installing the cord. If you accidentally over or under-tension the spring that handy notch makes it a simple fix without untying any knots.
Lou
I've never needed to replace a pull cord. I have tightened umpteen droopy pull ropes.