There is aBatch changebutton in the customer list. It allows to make similar edits in selected fields for all currently selected customers. To use this function, select necessary customers (by holding Ctrl or Shift keys) and clickBatch changebutton. The following popup window will appear:
TickActivecheckboxes of those fields you'd like to apply changes to. Then provide corresponding values on the right of each marked checkbox.
When you are ready, click OK button, and new values will be written to selected fields off all currently selected customers.