depend how much durability you increase can you make item, same how is in potions"healing/mana/sd"
You change it usually on item.bmd and item.txt, it should be on the last part, but if you get confused just use arrow as a reference, if you are using MuEmu, I think there should be something like ItemStack.txt aswell.
You mean, you need the item making command and having durability for this? Check server commands file.
Have it appear on shop, I guess. unless I'm not understanding this situation properly, haha.