Current version of TNet I'm using for Sightseer explicitly disallows multiple players from using the same save file to avoid this kind of confusion.
SetServerData can be used by admins for important stuff that players should not be able to change - configuration, message of the day, etc.
SetChannelData in a common channel (such as the global chat channel) can be used for player-settable configuration.
Keep in mind that all players have access to all other players' data, as long as they are in the same channel -- so SetPlayerData will work too.