I’m confused as to what you’re asking for. The list of Radio.net stations is provided by Radio.net, and not by Sonos. There are occasions where stations change their streaming URL, which would cause a “favorite” to fail, but navigating to it within the normal Radio.net interface should work, and you’d just want to update the “favorite” so it picks up the URL change.
You may want to disconnect Radio.net, then re-connect, which would force an authorization and data reload with the data on the Radio.net servers, too….but that’s still not Sonos servers.
Am I misunderstanding you? If so, I apologize, please let me know.