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

       /NEW_VERSION (default)
       /NONEW_VERSION

    Controls whether a new version of the patched file is created
    or the contents of the existing file are modified in place. The
    /NEW_VERSION qualifier is used in conjunction with the /ABSOLUTE
    qualifier to control whether a new version of the patched file
    is created or the contents of the existing file are modified
    in place. /NEW_VERSION is the default. If /NONEW_VERSION is
    selected, the PATCH command UPDATE will act as a checkpoint
    operation, that is, all modifications made to the file are
    written back to the file instead of waiting until image exit.
    If /ABSOLUTE is not specified with /NONEW_VERSION, /NONEW_VERSION
    is ignored, that is, a new version of the file will be created.
    /NONEW_VERSION will need to be used when patching large data
    files when there is not enough disk space to create a new version
    of the patched file.

                                   NOTE

       If /NEW_VERSION is specified, the file will be overwritten.
       No attempt on the part of the user, including pressing
       Ctrl/Y, will prevent this result. Therefore, you should
       have a back up copy of the file before making any attempt to
       patch it.

       PATCH will always issue an informational message at image
       exit, indicating that the file is being overwritten.