Just one little thing... I am sorry if you already know this... but you have to be Server Admin, not channel operator. And, that is not all you have to be, you must be U:Line:
U:lines are entries which define what addresses are allowed to log on as a server, as opposed to being logged on as a user or as an ircop/netadmin.
svsnick - changes a user's nick.
Example: svsnick Clueless HaveAClue - changes nick Clueless to HaveAClue.
This is the command that servers use to relay nick changes to each other.
Sorry if you knew this.
Note: That's for Unreal IRCD.