Question

Do you know if there is a way in Magento to override classes from Zend framework using configuration like in next example:

<config>
    <global>
        <models>
            <mymodule>
                <class>MyNamespace_MyModule_Model</class>
            </mymodule>
            <zend>
                <rewrite>
                    <somezendclass>MyNamespace_MyModule_Model_SomeZendClass</somezendclass>
                </rewrite>
            </zend>
        </models>
    </global>
</config>

Answer 1

I don’t think it is possible.
If you really want to change some class from ZF, you should copy it to app/code/local/Zend (path to your class…) directory.
Bad thing is that you should copy and paste whole class.