Excluding core files rewriting/editing

[coresh]

Should be excluded rewriting/editing core files. To add new tab should be uses layout updates. See how it is done for bundle products:

<adminhtml_catalog_product_bundle>
    <reference name="product_tabs">
        <action method="addTab"><name>bundle_items</name><block>bundle/adminhtml_catalog_product_edit_tab_bundle</block></action>
        <action method="bindShadowTabs"><first>bundle_items</first><second>customer_options</second></action>
    </reference>
</adminhtml_catalog_product_bundle>

src: http://stackoverflow.com/questions/9501622/magento-added-tab-gives-option-menu-to-include-closing-ul-and-div