Populate Audit Table via BN47 Form UserExit

Our Benefits department has asked us to build a process that will update a custom audit table anytime Beneficiary data is changed via BN47.  This seems like a perfect use for a Form UserExit, but I've never built one of these so I have a question.

It seems to me that an "End" user exit is the logical place to put my logic, since it is after the form  transaction has completed successfully.  However, it appears that when the End UserExit runs, all the LINE-FC values have already been cleared, so I can't tell what lines have been changed. Is this correct?

Do I need to move this logic to a "Middle" UserExit, and/or store the values in the Middle UE and then do the table update in the "End" UE?

Just curious what others have done.

Thanks!

Kelly