You can use your own icons by creating a $conf['wysiwyg_icons'] array in your settings.php.

The default icon list looks like this:
array(
  'icon1' => array('Love', 'love.gif'),
  'icon2' => array('Kiss', 'kiss.gif'),
  'icon3' => array('Cake', 'cake.gif'),
);

Setting $conf['wysiwyg_icons'] overrides the above list.

Define your icons as:
array-key-name => array(iconname, iconfilename.gif).
a. array-key-name: always icon99, where 99 is a number from 1 and up).
b. iconname: name in the toolbar and body text.
c. iconfilename.gif: name of the icon in directory /images.


Example:
$conf['wysiwyg_icons'] = array(
  'icon1' => array('Love', 'love2.gif'),
  'icon2' => array('Candle', 'candle.gif'),
);

There is no known limit in the number of icons you can define.

The icons are shown in the toolbar in the array order.
The array-key-names don't have to be successive but should 
always read icon99

When you update the $conf['wysiwyg_icons'] array, you should re-save the
buttons/plugins definition in admin/settings/wysiwyg.

You can also set $conf['wysiwyg_icons_path'] if your icons are not inside icon modules /images folder.
All icons have to be moved to the folder set in $conf['wysiwyg_icons_path'].
