I have to modify the xpath of Odoo module in my custom module. Consider below this code of website_sale module of V11 (For simplicity, i have reduced code):

<template id="recommended_products" inherit_id="website_sale.product" customize_show="True" name="Alternative Products">
    <xpath expr="//div[@id='product_full_description']" position="after">
        <div class="container mt32" t-if="product.alternative_product_ids">
            <h3>Alternative Products:</h3>                                        
        </div>
    </xpath>
</template>

For example, I want to replace

1) position="after" to position="before"

OR

2) expr="//div[@id='product_full_description']" to expr="//div[@id='product_small_description']"

How can i do this?