/sys$common/syshlp/helplib.hlb BACKUP Command, Qualifiers, /REPLACE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Output File Qualifier

    When you use /REPLACE in a copy or restore operation, and an
    identically named file exists in both the input and output
    specifiers, BACKUP performs the following tasks:

    o  Copies or restores a new version of the file with the same
       directory specification, file name, type, and version number

    o  Deletes the copy of the file that previously existed on the
       output disk

    In this way, the previous copy of the file is replaced with the
    restored version. Note that the version number is not incremented
    because the old copy of the file is deleted. If you want to keep
    the versions from both the input and the output specifiers, use
    the output file qualifier /NEW_VERSION.

    If you do not use /REPLACE, /OVERLAY, or /NEW_VERSION, and the
    version number of the file being restored is identical to the
    version number of the existing file, BACKUP reports an error and
    does not restore the file.