- Untie or cut the knot in the handle. Remove the handle.
- Attach (stitch or tape) the old rope to the new one where the handle was. You may do without this step, but it will make your life easier.
- Heel the boat so that the hull you are working at lifts about 3 or 4 ft.
- Lower the CB until you can reach the lifting rope from the bottom. The spring will keep the CB from falling.
- Pull the old rope from the bottom, cut the stitch/tape and tie the new rope to the CB as before.

Repeat for the other side.

Two tips: make thin and neat tail finishes in the new rope before changing and use very low stretch line.

I never did it in the water, but I guess it is feasible in shallow water as well as in dry ground.