If there are variations or exceptions that must be managed via or related by the sales order or invoices, there are a few things you can use.
1. Use Event Comments
Event comments may be made at the bottom of the Event Detail screen and printed on the sales order.
1. Navigate to the Event Detail screen
2. Scroll down to the comments section
3. Leave your comment
4. Click the print button to add the comment to the sales order. 
2. Leave Instructions in the Email to the Facility.
All fields of the attachment email sent to the facilities containing the Sales Order or Invoice are editable. So you may leave any instructions or special communications in the body of the email when you send it.
3. Edit PDF
If you cannot manage your goal using the options provided, you may also download the sales order or invoice as a PDF and open in a 3rd party PDF editor. This way you can add any text you require and make modifications to the PDF as needed.
4. If all else fails...
If you are looking for a design change, to add a field, or change the text of the sales order or invoice form, we may be able to accommodate Custom Templates at an additional cost. Please contact your Customer Success Manager or submit a ticket for more information.