For those of you unfamiliar with the "Site Editor", this was a web based file manager used to manipulate/create/delete files for Ning networks. To help improve security and prevent Network Creators from accidentally deleting files from their networks, we will be disabling the "Site Editor" interface this coming weekend.
Going forward, you must use SFTP or WebDav to view and make changes to your network's file system.
"...two of the most popular uses of the Site Editor will still be accessible through a web browser—the ability to redirect your Ning.com address to a domain mapped URL and the addition of "Pages" as tabs on your network. We will update the Developer Network and Ning Help Center with instructions later this week."
You should be able to upload the favicon the same way - just SFTP or WebDav into the site using the instructions listed above, and copy your file named favicon.ico into the default directory. Your favicon should work from there.
URL Mappings will still exist, as for Roles, AFAIK, the web interface to create new roles will be MIA for some time after this release, I will update this thread as soon as I get more info about the future of the Roles management web interface.