<%=146%> meta-tag is directly in between other HTML tags, I can override this variable with a custom script that will perform the customizations to the sign in page. This allows me to easily (ab)use property #146 as a built-in hook that will allow for a tailored sign in page that is customization-free.
Managing custom property #146 via the text.properties file is undesirable as I want the ability to change the injected script without having to have access to the web server file system. Fortunately, we are able to use the Custom Properties tab on the Web Profile Configuration page in the PIA to override the value for property #146. We do not need to worry about the value defined in the text.properties file as the value specified on the web profile will take precedence. You will simply need to set the Property Name to 146, Validation Type to String and Property Value to the custom script to modify the signin.html page. As you can see from the picture below, you can append the script to the desired footer text so that you do not lose out on the message from getting displayed at the bottom of the sign in page.
Here is how the sign in page looks from storing the above fragment in the web profile custom property: