That could help, but the pictures you provided do not look very reassuring. If you can get him to eat some feed, and drink some warm electrolyte fluids you might see how he does, but if he still shows a reluctance to eat or drink, and continues on producing the droppings, I would contact the vet.
Could you post a picture of the droppings?
Bright green droppings in birds can often be a sign that they are not eating enough. The greenish color is due to a bile pigment known as biliverdin. If the duck has been eating greens, that may have also caused a green look to the feces. If you are...
Epsom salts in a dilute enough solution would not damage the wound bed. Alternatively, you could use a poultry spray product or an antibacterial ointment