I'm trying to write 'quantity' or 'price_unit' in invoice_line_ids but it don's work

def process_invoice(self):
    self = self.with_user(SUPERUSER_ID)
    order_ids = self.order_ids.filtered(lambda order: order.state == 'draft')
    for order in order_ids:
        order.action_confirm()
        moves = order._create_invoices(final=False)
        for move in moves:
            new_quantity = 1
            new_price_unit = 200
            for line in move.line_ids:
                line.write({
                    'quantity': new_quantity,
                    'price_unit': new_price_unit
                })

I think I need to use _get_price_total_and_subtotal() and _get_fields_onchange_balance() functions but how to do it? THANKS