Can you create subsets of customers, for example, csv import of new customer list I want to keep sep

[Haberdash]

We are going to do a special project with one large customer to send items to THEIR list of customers. We see how to create a CSV list, but we want to keep them separate from our day-to-day regular customers. How do we create a separate list of customers for this project?

[IP1999]

You can use customer tags or Meta Fields to accomplish this. 

[IP1999]

You may want to look at this as well

https://help.shopify.com/en/manual/customers/customer-segmentation