I found a way to change the logo on the ‘continue to login’ page (as shown in the original post) and on the ‘logged out page’… using CSS to replace images and backgrounds (Ignition v8.1.18). Note however it does not apply to the username/password entry pages.
See linked post:
https://forum.inductiveautomation.com/t/how-to-customize-perspective-login-logout-pages-with-css-partial-success/63275