User-exit for VA21

I'm doing a functional spec for an enhancement to copy the valid from date in VA21 to the valid-to date + 14 days. Does anywone know what user-exit that can be used for the enhancement.

Thanks,

hi
these are the avilable user exits and BAdis.. for VA21.

codeV60F0001 SD Billing plan (customer enhancement) diff. to billing plan
V46H0001 SD Customer functions for resource-related billing
V45W0001 SD Service Management: Forward Contract Data to Item
V45S0004 Effectivity type in sales order
V45S0003 MRP-relevance for incomplete configuration
V45S0001 Update sales document from configuration
V45P0001 SD customer function for cross-company code sales
V45L0001 SD component supplier processing (customer enhancements)
V45E0002 Data transfer in procurement elements (PRreq., assembly)
V45E0001 Update the purchase order from the sales order
V45A0004 Copy packing proposal
V45A0003 Collector for customer function modulpool MV45A
V45A0002 Predefine sold-to party in sales document
V45A0001 Determine alternative materials for product selection
SDTRM001 Reschedule schedule lines without a new ATP check
SDAPO001 Activating Sourcing Subitem Quantity Propagation

Business Add-in
BADI_SD_SCH_GETWAGFZ Scheduling Agreement: Read WAGFZ from S073
BADI_SD_V46H0001 SD Customer functions for resource-related billing[/code]