Instructions
Enter the control menu if you are a guild lead. This menu contains an easily accessible button to allow changes to guild messages. The button appears like a pencil-type icon.
Click the message-editing button, then type in the new message to display to the guild.
Contact game customer support for assistance if the editing button is not present or has been grayed out. Players have reported both of these problems in some cases. Other have reported situations in which the button is appears normal, but does not allow changes to the guild message.