Hi,
You can add an automated action inside the database for the same. Set up an automated action, such a way that on meeting certain condition it will create an extra line in order.

The above attached is a sample, you can change the code as per the need

if not env.context.get('skip_iteration'):

  for record in records:

    vals = {

      'product_id': record.product_id.id,

      'product_uom_qty': record.product_uom_qty * -1,

      'price_unit': 1,

      'order_id': record.order_id.id,

    }

    env['sale.order.line'].with_context(skip_iteration=True).create(vals)

Thanks