Updating Billing Blocks within Billing Plans

Hi all,

I have to update the bililng block within a billing plan but cannot see a way of doing this. Can someone help?

I currently have:

CALL FUNCTION 'SD_SALES_DOCUMENT_READ'
     EXPORTING
       DOCUMENT_NUMBER            = P_ST_CONTRACTS_SALES_DOC
       SUPPRESS_AVAILIBILITY_DIA  = 'X'
       SUPPRESS_TEXT_POPUP        = 'X'
       I_BLOCK                    = 'X'
       STATUS_BUFFER_REFRESH      = 'X'
       REQUISITION_BUFFER_REFRESH = 'X'.

   CALL FUNCTION 'SD_SALES_ITEM_READ'
     EXPORTING
       ITEM_NUMBER         = P_ST_CONTRACTS_SALES_ITEM
     EXCEPTIONS
       ITEM_NUMBER_MISSING = 1
       OTHERS              = 2.
   IF SY-SUBRC <> 0.
* Implement suitable error handling here
   ENDIF.

   CALL FUNCTION 'SD_SALES_BILLINGPLAN_READ'
     EXPORTING
       I_VBELN                = P_ST_CONTRACTS_SALES_DOC
       I_POSNR                = P_ST_CONTRACTS_SALES_ITEM
     IMPORTING
       E_FPLA                 = st_fpla
     TABLES
       E_FPLT                 = p_t_billing_items
     EXCEPTIONS
       NO_BILLINGPLAN_ALLOWED = 1
       NO_BILLINGPLAN_FOUND   = 2
       OTHERS                 = 3.
   IF SY-SUBRC <> 0.
* Implement suitable error handling here
   ENDIF.

=======================

This populates p_t_billing_items with the billing schedule and I can manipulate its contents to add/remove billing blocks:(field FAKSP). How can I save my changes?

Cheers,

Russ.