Here too, adding a record is really updating a dummy record already in the data set. The main difference is that dummy records cannot be written automatically when the data set is allocated. You will have to use your own method for flagging dummy records. The update form of the WRITE macro (MACRF=W) must be used rather than the add form (MACRF=WA).

You will have to retrieve the record first (using a READ macro), test for a dummy record, update, and write.