copy records from one file to another

I wonder if I've missed the obvious...  Don't let my subject mislead you -
I can't use CPYF for my task.

I am basically copying information from one file to another, but some of
the data needs to change, and I need to break out (create) detail records
where there are summary.

I can get all of the detail records.  My question is about copying the
fields from one file to another.  I started with two identical files (as
far as field layout goes.)  I used PREFIX on one so I wouldn't have
conflicting field names in the program.  I was thinking I could just EVAL
NEWFILE=OLDFILE on the format names, but that didn't work.

Can it be done with EXTNAME data structures?

Or do I have to copy each field individually before I can write the
record?  (Is this what the MOVEC vote was for on the ballot?)

Thanks!