Works on v2.4.7 and v4.1.6
Details on my mod to Quick Tags plug-in.

I have added a fourth <div> as follows:
1. Open _mytags.plugin.php and edit
2. In function GetDefaultSettings() copy existing div code, that starts as follows and changing div numbers. Do not change ['rows' => 4]

'moretags_div1' => array(

3. In function SkinBeginHtmlHead() copy code for div starting as follows, and change numbers to suit step 2 above.

if ( $this->Settings->get('moretags_div1') != '' )

4. In function AnotherButton(id, display, tagClass, tagStart, tagEnd, tit, open)
copy code for new button, as follows and again change div number to suit above. The 'd1' is the button label(text) and can be anything. I have used 'Cl' on a button to {clear:both} and 'dL' for a <div> that has {float:left} in it's CSS class.

MoreButtons[MoreButtons.length] = new AnotherButton(
'mtb_div1','d1','divs leftgap','

5. Then edit the plug-in via management ~ pluin installed ~ MyTags to create the style wanted.

OK All the above was unnecessary. clearboth is already a class in rsc/css/basic.css and I made two more classes to replace the divs made above; post_fll and post_flr (post detail float left and ditto float right). So the divs can be used for something else. Well at least they are implimented and the css of each cna be easily changed.