Access to Export Data in a User-Defined File Layout 
Use
You can set up user exits in different areas (for example, structure, block) within the file layout. If the
change validation functions provided do not meet your requirements, you can define customer user exits. In your user exits, you use the function modules included in the standard system to define your change validation function.Features
You can use the function module within the file layout to enter data for the structures (NEW_ and OLD_ structures) that already exist in the export program for the change validation user exit. SAP recommends that you use this procedure in the following situations:
The standard system contains the following function modules:
This function module must be called once before all other function module. You must enter the current program name for the Interface Toolbox.
This function module enters data in the OLD tables in the same way as the Import function (IMPRT with specification L).
This function module enters data in the OLD tables in the same way as the Import function (IMPRT with specification O).
This function module enters the current result in the NEW tables.