Custom Pricing Mass Update or CSV Import

I am able to mass update item pricing via mass updates just fine. The issue I am having is when trying to update a customer's "custom" pricing on the customer record via mass updates or a CSV import. So, I guess this is a 2 part question:

1) I've looked but could not find one. Is there a mass update that will allow me update CUSTOM pricing, and filter the mass update records based on some criteria (such as fields on the item record)?

2) I've created some CSV files for import to update the existing CUSTOM pricing on the customer record. However, when I import the CSV files I always get the result error "This entity already exists". I have triple checked that the "update" option is selected on the import. Is this a glitch in NetSuite, or does anyone know of a better way do this?