VMS Help EXCHANGE, COPY, Qualifiers, /REPLACE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /REPLACE
       /NOREPLACE

    Requests that if an RT-11 output file already exists with the
    same file specification as that entered for the output file, the
    existing file is to be deleted before the copy proceeds. COPY
    allocates new space for the output file. The /REPLACE qualifier
    is valid for RT-11 output only; it is equivalent to the RT-11
    COPY command qualifier /PREDELETE.

    By default, COPY creates the new file first and then, after the
    copy operation is done, deletes the previous file. However, when
    you use /REPLACE, COPY deletes the previous file before it copies
    the new file. This can be a problem if the input file has been
    corrupted because the previous version of the file will have been
    deleted. Therefore, you should use /REPLACE only when there is
    insufficient room for two copies of the file.