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

    Controls whether the new generation of the element created by the
    replacement is reserved. If you specify the /RESERVE qualifier,
    the generation is reserved and the element files are not deleted
    from your current default directory. The list of concurrent
    replacements is updated as if /RESERVE had been omitted.