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/discount/discountcode1 

That would take you to the store and use that discount code at checkout.

How to:

1. Add your Store URL

2. Add /discount/

3. Add discount code to the end

---------Domain--------------/discount/-------code------

test123.myshopify.com   /discount/   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.