Magento products per page dropdown

I have a problem with products per page. I have task to edit values of category products per page dropdown. I know that I can edit them by System->Configuration but my teacher said that I have to use local.xml.

After research I found this theme Setting 10 products per page in magento that says:

Just go to the app\design\frontend\base\default\layout\catalog.xml and go to the line number 85

and find catalog/product_list_toolbar just modify ur xml according to ur need.

I have tried this. This is my code. After I save everything, it doesn't change values. Where is my problem?

P.s. my cache is turned off.

**

<collection_index_index>
    <reference name="content">
        <block type="collection/collection" name="product_list" template="catalog/product/list.phtml">
            <block type="catalog/product_list_toolbar" name="product_list_toolbar" template="catalog/product/list/toolbar.phtml">
                <block type="page/html_pager" name="product_list_toolbar_pager"/>


                    <action method="setDefaultListPerPage"><limit>4</limit></action>
                    <action method="setDefaultGridPerPage"><limit>9</limit></action>
                    <action method="addPagerLimit"><mode>list</mode><limit>2</limit></action>
                    <action method="addPagerLimit"><mode>list</mode><limit>4</limit></action>
                    <action method="addPagerLimit"><mode>list</mode><limit>6</limit></action>
                    <action method="addPagerLimit"><mode>list</mode><limit>8</limit></action>
                    <action method="addPagerLimit" translate="label"><mode>list</mode><limit>all</limit><label>All</label></action>

            </block>
        </block>
    </reference>
</collection_index_index>

**