the default state is:
<a href="./" class="dynamic dynamic-children menu-item"><span class="additional-background"><span class="menu-item-text">Présentation</span></span></a>
so if class = rfr-opened add alt=”open”
<a alt="open" href="./" class="dynamic dynamic-children menu-item rfr-opened"><span class="additional-background"><span class="menu-item-text">Présentation</span></span></a>
so if class doesn’t have rfr-opened add alt=”close”
<a alt="closed" href="./" class="dynamic dynamic-children menu-item"><span class="additional-background"><span class="menu-item-text">Présentation</span></span></a>
Something like this?
Demonstration: http://jsfiddle.net/9xLYV/