gistfile1.txt

<?xml version="1.0" encoding="utf-8"?>
<frontend>
    <routers>
        <newsletter>
            <args>
                <modules>
                    <extension_tag before="Mage_Newsletter">Company_Extension_Newsletter</extension_tag>
                </modules>
            </args>
        </newsletter>
    </routers>
</frontend>

<global>
    <blocks>
        <extension_tag>
            <class>Company_Extension_Block_Subscription_Messages</class>
        </extension_tag>
        <core>
            <rewrite>
                <messages>Company_Extension_Block_Core_Messages</messages>
            </rewrite>
        </core>
    </blocks>
</global>

<layout>
    <updates>
        <extension_tag>
            <file>company_extension.xml</file>
        </extension_tag>
    </updates>
</layout>