Modifying child block using Custom Layout Update XML

I am currently using a CMS Block to add more details on my product page. I had the following block (product_custom) added inside catalog.xml:

<catalog_product_view translate="label">
    <!--- ... --->
    <reference name="content">
        <!--- ... --->
        <block type="catalog/product_view" name="product.info" template="catalog/product/view.phtml">
            <block type="cms/block" name="product.info.custom" as="product_custom">
                <action method="setBlockId">
                    <block_id>product_custom</block_id>
                </action>
            </block>
        </block>
    </reference>
</catalog_product_view>

Now, I want other products to show different content, so I created another block (product_custom2) and use Design > Custom Layout Update:

<reference name="content">
    <block type="catalog/product_view">
        <block type="cms/block" name="product.info.custom" as="product_custom">
            <action method="setBlockId">
                <block_id>product_custom2</block_id>
            </action>
        </block>
    </block>
</reference>

Unfortunately, the product page is showing previous block instead of the new one. Did I miss something on the custom layout xml? Or is it not allowed? And what would possibly the best solution to this one?

Thanks for the replies.