Hi Peter,
You can go to the transaction BUS3.
Select the view BUP520 - Identification Numbers.
Double click on Further checks in Dialog Structure on the left.
Click on New Entires and input for Application name BUP and for Function module After Entry (PAI) name of your custom function module that will contain logic for checking of identification number.
Per example if you want to check Social Security Number, create custom FM which will contain
calling of FM BUP_BUPA_BUT0ID_GET with which you can get the identification data which contains identification number and type that needs to be checked.
Then loop at BUT0ID returned from the above FM. Check ifBUT0ID-type is equal to IBS001. If it is(Social Security Number) write the logic for checking BUT0ID-idnumber.
Hope it helps.
Kind regards,
Marko