No, it's a running change ... your new UserID will simply replace the old one.
However, you may want to let fellow guildies know that your user name changed ... in case that impacts any out-of-game guild tracking, etc.
"May you walk on warm sands."
"First, I would ask that you look to the poor and the suffering around Cyrodiil. Look into their hearts, and then look into your own."
"May Auri-El's light guide you in your darkest hours."