Hi,
In order to achieve this, you have to inherit the portal template and apply the changes from an inherited view directly in the db or from a custom module.

* Enable Developer Mode
* From Settings -> Technical -> User Interface -> Views
* Search and open "Sales Order Portal Content" view, external id: sale.sale_order_portal_content
* This is the view responsible for the portal
* Now you have to modify this template as per the need
* Create an inherited view, locate the needed node using xpath expression
* Apply the changes

Thanks