custom-extension.xml

<extension>
  <modules>
    <module>
      <id>Customizing Alfresco Share Header</id>
      <version>1.0</version>
      <auto-deploy>true</auto-deploy>   
      <customizations>
        <customization>
          <targetPackageRoot>org.alfresco.share.header</targetPackageRoot>
          <sourcePackageRoot>com.alvexcore.header</sourcePackageRoot>
        </customization>
        <customization>
          <targetPackageRoot>org.alfresco.share.pages</targetPackageRoot>
          <sourcePackageRoot>com.alvexcore.header</sourcePackageRoot>
          <alwaysApply>
            <webscript>share-header</webscript>
          </alwaysApply>
        </customization>
      </customizations>
    </module>
  </modules>
</extension>