First, it is a very bad idea to overwrite a data set.
Now, suppose your requirement is to create a second data set, with the records in reverse order from the first. For a PS data set or a VSAM ESDS, you're better off using your sort product; put a counter on the end of the record and then sort in descending order.
For a VSAM KSDS, perform a logical NOT on the key.
"You have sat too long for any good you have been doing lately ... Depart, I say; and let us have done with you. In the name of God, go!" -- what I say to a junior programmer at least once a day