@aweegander
Right, but you also need to change in same file line:
<h2 id="show_hide_seo"><div id="ic" class="s-plus"></div><span><?php _e('Meta Options (advanced)', 'all_in_one') ; ?></span></h2>
Into:
<h2 id="show_hide_seo"><div id="ic" class="s-minus"></div><span><?php _e('Meta Options (advanced)', 'all_in_one') ; ?></span></h2>
(to get correct plus-minus sign)