Best way to bulk import CAS users from different site

I need to import a number of users who are set up on another site. I believe they all have NetIDs, so I could create a view that simply gives me a list of their NetIDs, and then copy and paste the NetIDs in the “Add CAS User(s)” field of the new site. However, there are custom fields and additional data that have been added for the users on the original site, and if I just create them as new CAS users on the new site, I’ll be missing all that additional data. What’s the best way to approach this? Is there a way to create all the users by importing from a Views data export file that includes all the custom fields - or is it best to create the users as fresh CAS users and then somehow import the additional data into those user records?