@Didier
Try this approach:
function afterrender(sender, eOpts)
{
var repStr = '<tpl if="icon.iconStr"><span class="{icon.iconStr}"></span><tpl else><img style="margin-top:3px;width:16px;height:16px;" src="{icon.iconUrl}"/></tpl> {val}';
sender.listConfig.tpl.html = sender.listConfig.tpl.html.replace('{val}', repStr);
}