Is there any way to modify this tracking.phtml on magento admin?

When we choose one of the option below, the field 'title' automatically filled with selected value from carrier options.

I want to do the same for 'number' field, it would be filled with something when I choose my custom carrier. Is there any way to modify this tracking form? If yes, how?

Thank's in advance

Add following observer in your module's config.xml

             <events>
                <adminhtml_block_html_before>
                    <observers>
                        <add_script_on_shipment>
                            <class>yourmodule/observer</class>
                            <method>addScript</method>
                        </add_script_on_shipment>
                    </observers>
                </adminhtml_block_html_before>
            </events>

Put following code in Observer.php

public function addScript($observer) {
    $block = $observer->getEvent()->getBlock();
    if (($block instanceof Mage_Adminhtml_Block_Sales_Order_Shipment_View_Tracking) && $block->getType() != 'core/template' /*&& is your carrier active*/) {
        $shipment = $block->getShipment();
        $_child = clone $block;
        $_child->setType('core/template');
        $block->setChild('calling_block', $_child);
        $block->setTemplate('yourmodule/custom_script.phtml');
    }
}

add following code with required modifications in custom_script.phtml

<?php echo $this->getChildHtml('calling_block');?>
<script type="text/javascript">
     /*your custom javascript code to bind onchange event*/
</script>