\unprotect
\setvalue{\??itemgroupkeyword\v!no\v!repeat   }{\setfalse\c_strc_itemgroups_repeat}

\def\strc_itemgroups_check_for_repeated
  {\ifconditional\c_strc_itemgroups_repeat
      \ifx\m_strc_itemgroups_repeat_start\empty
        \edef\m_strc_itemgroups_repeat_start{\currentitemlevel}%
      \fi
   \else
      \let\m_strc_itemgroups_repeat_start\empty
   \fi}
\protect

\setupitemgroup[itemize][broad,joinedup,packed,autointro]
\starttext
\setupitemize[itemalign=flushright]
\startitemize[n,repeat]
  \item level a
    \startitemize[n,norepeat]
      \item level b
        \startitemize[A]
          \item level c
        \stopitemize
    \stopitemize
\stopitemize
\stoptext