You can assign private members into groups and give them permissions to access the podcast channels that are associated with the groups.

Important! You should create the groups before you batch add members for groups. Private members cannot be assigned to non-existent groups.

In the .txt file, add the [Group Name, Group Name2, Group Name3 ] after the email for each line. Separate multiple group names with commas. Please see the example file here. 

You can also set default passwords for your private members with groups. Please see the example file here.