To Unsubscribe customers from the generic customer list:
If you import unsubscribed customers in a new list, the system will skip those from the transaction list. You will receive the count of skipped customers after you import the transactions.
The status of the customer can be Active or Unsubscribed
To check the status, Go to Customer Experience » Deploy » Customers » Customer list and click on the email address of that customer. Refer to the image below: