thanks for your help

The image you posted appears to be the XML data representation of a sale order, not the HTML source code of the rendered sales order page. On the sales order itself, right click and view the page source. I think you are looking for a DIV element with the class

uir-page-title-secondline

, which is the line containing the Sales Order Document Number, Customer Name, and Status. You'd likely be looking at adding an additional sub-element there.

It's working

Just be sure to keep a list of all scripts that modify NetSuite pages directly, and check/verify that they are still working after each major release (2020.1, 2020.2, etc.). NetSuite could change their HTML structure or CSS class names at any time, which might break any script that modifies the DOM directly.

good point