Sabotage all three executions.
Complete the mission "Money for Old Rope" by sabotaging each of the three executions:
Poison the tongs on the wagon with Bane or Lullaby potion.
Swap the rope in the barn loft with the rotten rope from Hermann.
Take the Executioner's Sword from the tent chest, run into Rattay and dull it on the blacksmith's grindstone, then return it to the chest.