Unlike the above poster who is an example of "those" people we don't need here, updating your Wii will not cause bricking if you are using a game of the same region. Also, the new config that Wiikey.cn released is compaitble with the 3.X firmwares. Going online does not affect anything with the Wiikey mod.
In the future, just look in this section and most likely there will be a thread about the new firmware and if it causes any issues with modchips. Of course you will have to weed thru crap posts like the one above by Tagg07