Add asterisk after labels in enumerate
\documentclass[a4paper]{article}
\newenvironment{modenumerate}
{\enumerate\setupmodenumerate}
{\endenumerate}
\newif\ifmoditem
\newcommand{\setupmodenumerate}{%
\global\moditemfalse
\let\origmakelabel\makelabel
\def\moditem##1{\global\moditemtrue\def\mesymbol{##1}\item}%
\def\makelabel##1{%
\origmakelabel{##1\ifmoditem\rlap{\mesymbol}\fi\enspace}%
\global\moditemfalse}%
}
\begin{document}
\begin{modenumerate}
\item uno
\item due
\moditem{*} tre
\item\label{four} quattro
\moditem{*}[\hfill\ref{four}.] quattro
\end{modenumerate}
\end{document}
\begin{enumerate}
\item One
\item Two
\item $\!\!\!\!{^*}$ Three
\item Four
\end{enumerate}
does the trick! Easy.
\!
moves the next text a tad to the left, use as many or few as to your preference.