Board Thread:Support Requests - Community Management/@comment-13918697-20140513022214/@comment-168424-20140513151231

Select all, cut, paste into a text editor, replace all, select all, copy, paste back into edit window.

Or you could find a browser with replace all functionality.

Lastly, Special:Contact/general and ask Wikia to put this functionality into their Visual Editor. Unlikely, but possible.