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

    Specifies that a new generation is to be created only if the
    input file is different from the generation that was reserved.
    By default, a new generation is always created, regardless of the
    existence of any differences.

    CMS deletes the input file from the specified location after
    the new generation is created (unless you specify the /KEEP or
    /RESERVE qualifier).