sale_order_view.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>

        <record id="sorp_view_order_form" model="ir.ui.view">
            <field name="name">sale.order.form</field>
            <field name="model">sale.order</field>
            <field name="inherit_id" ref="sale.view_order_form"/>
            <field name="arch" type="xml">
                <field name="order_line" position="after">
                    <button name="recalculate_prices"
                            string="Recalculate prices"
                            attrs="{'invisible': [('state', 'not in', ['draft', 'sent'])]}"
                            type="object" colspan="4" class="oe_inline"/>
                    <button name="recalculate_names"
                            string="Reset descriptions"
                            attrs="{'invisible': [('state', 'not in', ['draft', 'sent'])]}"
                            type="object" colspan="4" class="oe_inline"/>
                </field>
            </field>
        </record>

</odoo>