I run a patreon and I would like to give my patrons a discount for their purchase. However I would like to avoid them sharing the discount to other people so I was wondering if there was a way to make a customer segment using the CSV file from patreon.
You can tag the customers while importing, then just make a segment for those customers that have been tagged. But to create discounts that are customer specific you'd only need the tag I think, segment is optional.
To clarify my answer above, you can tag and segment the customers while importing, but the right moment to do it is while migrating the customers (importing customers that don't exist yet in Shopify).
If the customers already exist in Shopify you don't want to just import a new list. You'd need to export, filter the customers, import and overwrite adding a tag, which seems a bit cumbersome. In this case I think it's better relying on an import/export app to add the tag to the customers in your list, then use the tag to create the segment, and the discount to be segment specific: https://apps.shopify.com/search?q=import%20export