Hello @Dave W !
You can use this documentation - branding: Custom Page Title, Logo, and Favicon
Now you need 2 types of favicon - .svg and .ico
And yes, it will persist after updates.
Hello, Jessie!
Please provide more info, is it for admin or customer subscription?
Looks like there is no permission 'Enable hosting' in Service Plan -> 'Hosting Parameters' tab, or enabled 'Restricted mode' with disabled 'Hosting Management'.