To import multiple IP addresses from another source such an an Excel spreadsheet, first export to a .CSV (comma separated values) file.

i.e. 192.168.1.1,192.168.1.2,192.168.1.3...

Open the .CSV file in Windows Notepad and copy the contents and paste it into the "Add IP Addresses" field on the Account Settings page.  Click on Update Settings to apply your changes.