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

    If LBR$DELETE_KEY finds the key specified by key_name in the
    current index, it deletes the key. Note that, if you want to
    delete a library module, you should first use LBR$DELETE_KEY to
    delete any keys that point to it, then use LBR$DELETE_DATA to
    delete the module's header and associated data.

    You cannot call LBR$DELETE_KEY from within the user-supplied
    routine specified in LBR$SEARCH or LBR$GET_INDEX.