Board Thread:Support Requests - Community Management/@comment-31458771-20170328194654/@comment-9605025-20170329005815

You can edit any of the system messages listed here. The ones pertaining to chat all begin with "Chat-". As you might guess from Annabeth and Percy's reply, you edit a system message by editing the page "MediaWiki:system-message" where "system-message" is the name of the message.