Updating a contact list, sending reminder email to selected contacts

I would like to update the opt in/opt out for multiple contacts (based on demographics).  I tested this out by exporting the contact list, updating the ‘Unsubscribe’ column then importing back in.  But I am anticipating needing to merge in several hundred contacts and my organization can not grant me Manage Directories permissions for automatic deduplication. Therefore, it seems I need to click on Merge for each contact.  Is there an easier way to update the contact list, based on demographic Embedded data fields.  I wish there was a filter tool in contact lists.  Thank you!