The LDB won't help you a bit for getting records with a Changed On Date = SY-DATUM.
I'm not clear on exactly what you are trying to get is it: 1. Infotypes changed as of SY-DATUM with a Future Date or 2. Infotypes changed Today or Infotypes with a Future Date changed anytime,
For either one you are going to have add logic for each Infotype to do a Select PERNR from PAXXXX Where AEDTM = SY-DATUM and BEGDA > SY-DATUM then load that into a table. After you have finished selecting all qualified PERNRS then sort this table by PERNR and then do a Delete Adjacent Duplicates. After this loop through your table of PERNRS and load PNPPERNR. This should all be done before you do the GET PERNR.