So the MODIFY is just used to kick off the exit? Is there some other option you can use and write your own little exit just to pass the parameters on to the exit you actually want? (I have no idea, just poking).
I was given a spool file on tape(s) once. I can't remember if it was from POWER or JES3. The printsthop I took it took could read it (they had a tape drive and some little mini-computer attached to their fancy printing box) and just print it. With that file, I guess you could print first last and last first, if your spooler is then able to accept a file in spool format. I have no idea. And no, you wouldn't need to know much about the format. As long as there is some "new page" indicator at the start of a record, it could be done.