You can create shareable discount links that will automatically add the discount to the customer's cart but you need to manually create them.
Here's an example: https://www.test123.myshopify.com/discounts/discountcode1
That would take you to the store and use that discount code at checkout.
1. Add your Store URL
2. Add /discounts/
3. Add discount code to the end
test123.myshopify.com /discounts/ discountcode1
You do need to do this manually but if you do this in your CSV file, you should be able to expedite the process a bit.