I am not 100% sure where to move forward from here, but I can provide some basic information for others to build upon.
The code in the style:
<if condition="$show['managepost']"><div class="smallfont" style="float:$stylevar[right]"><a href="postings.php?$session[sessionurl]do=managepost&p=$post[postid]">$vbphrase[manage]</a></div></if>
<a href="member.php?$session[sessionurl]u=$post[userid]">$post[musername]</a>
</td>
</tr>
<tr>
<td class="alt1">
<div class="smallfont">
<phrase 1="member.php?$session[sessionurl]u=$post[del_userid]" 2="$post[del_username]">$vbphrase[message_deleted_by_x]</phrase>
<if condition="$post['del_reason']">$vbphrase[reason]: <em>$post[del_reason]</em></if>
This needs to be designed to allow/deny specific usergroups. From my understanding though, you first must display this for all users, then add a IF statement designating the usergroup (see below).
<if condition="!is_member_of($vbulletin->userinfo, X)">YOUR CODE</if>