XMLPUB - Invoice formatting options

Hi all,

         I would like to update the Invoice formatting options in;

Main Menu>Set Up Financials/Supply Chain>Product Related>Billing>Setup Invoice Options>Invoice Formatting Options> discounts,surcharges,taxes for invoie format "XMLPUB".but the page is set as display only and iam not able to perform changes unlike for the Invoice format SQR and other where we can edit and modify the changes. can someone explain me how to enable the page to modify the tax line options for XMLPUB. do we need to make the page enabled by some settings or do we need to apply the settings in anyother page to modify the tax Line options and other fields in the page for XMLPUB.