Is there a way to edit multiple customer contact security roles at once?

At my company, we have many clients in which we are changing their security roles based on the company they're from. I tested out the import feature to import many of our customer contacts. This worked out successfully, however they are all assigned the Default security role (understandable). We have a customer contacts list in the thousands, if I import them all am I expected to edit their security role individually one-by-one? 1. How can I edit the security roles of multiple contacts at once? 2. Is there a way I can assign an automatic security role to a Customer, that way when new contacts are added they fall in with the default security role given to the Customer?