How to add DFF or extrinsic field on OBN cXML Invoice doc

Summary:

Many of our suppliers send us invoices using OBN. Sometimes, some of them are charging a special charge or tariff and they put this amount under SpecialHandling line as we saw in the cxml. When this invoice was loaded in Fusion, this line item was shown as Miscelleneous charges.

We want to know - can we add an additional line type in OBN cXml invoice (and label it as Tariff) to capture the tariff charges and easily report it?
Also, can the same be implemented in ISP portal invoices as well?

Any help / pointer will be highly appreciated.
Thank you.