P, I'm not sure if that's possible, but I'm aware of a purge script I had a few years ago.

<?if($GROUP_ID$==4)?><a href="javascript://"onclick="new _uWnd('del_chat','Purge tag board', 350,130,{alert:1,autosize:0,modal:1,resize:0,nomove:1,max:0,fadespeed:500,align:0,oncontent:function(){del0()}},'<center><div class=\'del_c\'><div class=\'del_dels\'>Removed: 0</div><div class=\'del_num\'>All messages: <span id=\'num\'></span></div><center><div class=\'del_chat\'></div><div class=\'del_time\'></div></center></div><div id=\'del_ok\'>Tag board purged!</div><div id=\'del_error\'>The tag board is empty!</div><div id=\'del_enter\'><input type=\'button\' onclick=\'del1()\' value=\'Start purging\' /></div></center>' ;">Purge tag board</a>
       <style type="text/css">
       .del_chat {width:300px;height:15px;border:1px solid #666;background:#f2f2f2;margin:10px 0;} /* Progress bar border color and background */
       .delete_chat {height:15px;float:left;} /* Fill the progress bar */
       .delete_chats {padding:1px;background:#c0c0c0;height:13px;} /* style strip progress bar (main color) */
       #del_enter, #del_ok, #del_error, .del_c {margin:10px auto !important;overflow:none;} /* padding for the button and the message about the success / failure */
       #del_ok, #del_error {font-size:15px;} /* size of the text messages about the success / failure */
       #del_ok, #del_error, .del_c {text-align:center;display:none;} /* vyravnianie text messages about the success / failure */
       .del_num {text-align:left;margin-left:14px;} /* style total number of messages in the chat */
       .del_dels {text-align:right;float:right;margin-right:13px;} /* style of deleted messages */
       </style>
<script type="text/javascript" src="/del.js"></script><?endif?>1
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I have attached del.js.

Both might be possible with custom scripting, which I can't provide, unfortunately.