You do not have to create POs through the Detailed PO Module. Use it for your benefit as much or as little as you wish.
Discounts do not have to be permanently active on your site. To manage which discounts are active and which are not use the toggle on the main discounts page.
You can make edits to your discount's information at any time. Just select the gear icon at the end of the discount's row to begin making any updates.
To delete any old discounts just select the red X on your main discounts page to remove it. This will permanently delete the discount and you will have to recreate it if you wish to use it again.