To edit a breadcrumb from the block, you can simply do that :
class Adin_Sales_Block_Invoice_View extends Mage_Core_Block_Template
{
private $_mainOrder;
public function _prepareLayout()
{
if ($breadcrumbs = $this->getLayout()->getBlock('breadcrumbs')) {
$breadcrumbs->addCrumb('All orders', array('label'=>$this->__('All my invoices'), 'title'=>$this->__('All my invoices'), 'link'=>$this->getUrl('sales/invoice/history')));
$breadcrumbs->addCrumb('My order', array('label'=>$this->__('My invoices : order %s', $this->_mainOrder->getIncrementId()), 'title'=>$this->__('My invoices : order %s',$this->_mainOrder->getIncrementId()), ));
}
return parent::_prepareLayout();
}
$_mainOrder is defined in the __contruct() function