well, actually, with the Activity Launcher you can launch the System Update app settings and change the download server to another one, but I have no idea about their purpose. One is fOTA, there's also fOTA-test and fOTA-dev and another one besides the default one. They're region dependent too, so you get different servers depending on the rom you have.
I do not intend to try that, it sounds even more risky to download a test update..