You can cancel the prenotification and make your changes in the same prenotification. You then resend the prenotification.
Please note: every prenotification is given a unique label within HCN by which Portbase recognises the transaction. You can change, cancel and resubmit this prenotification with a unique label at any time. As long as you continue to use the same original prenotification, you pay for only one transaction.
View the Functionality Matrix to see whether the terminal supports a modification message.
You can change your permissions via 'customise preferences'.