VMS Help LBR Routines, LBR$REPLACE_KEY, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    If LBR$REPLACE_KEY does not find the key in the current index,
    it calls the LBR$INSERT_KEY routine to insert the key. If
    LBR$REPLACE_KEY does find the key, it modifies the key entry
    in the index so that it points to the new module header.