Hi,
The user exits SDVFX007, SDVFX008 might be useful in your case. The list of exits is:
SDVFX001 User exit header line in delivery to accounting
SDVFX002 User exit for A/R line in transfer to accounting
SDVFX003 User exit cash clearing in transfer to accounting
SDVFX004 User exit G/L line in transfer to accounting
SDVFX005 User exit reserves in transfer to accounting
SDVFX006 User exit tax line in transfer to accounting
SDVFX007 User exit: Billing plan during transfer to Accounting
SDVFX008 User exit: Processing of transfer structures SD-FI
SDVFX009 Billing doc. processing KIDONO (payment reference numbe
SDVFX010 User exit item table for the customer lines
SDVFX011 Userexit for the komkcv- and kompcv-structures
Cheers,
Arindam