create a new template in the /views/category/tmpl folder
would be preferable in templates/YOUR_TEMPLATE/html/com_virtuemart/category
you can also over-ride the sublayouts in
templates/YOUR_TEMPLATE/html/com_virtuemart/sublayouts
the sublayouts are called by
echo ShopFunctionsF::renderVmSubLayout('categories',array('categories'=>$this->category->children));
so you could try
echo ShopFunctionsF::renderVmSubLayout('
categories2',array('categories'=>$this->category->children));
and make a
categories2.php in templates/YOUR_TEMPLATE/html/com_virtuemart/sublayouts