open js file
./clientscript/ckeditor/plugins/editingblock/plugin.js
Find:
Code:
CKEDITOR.config.startupMode = 'wysiwyg';
Replace with:
Code:
CKEDITOR.config.startupMode = 'source';
Enjoy.
Keep in mind, while in source mode, copying content from somewhere else (such as articles etc) that have images, tables etc, the "extra" content will not copy over. Linked content will not copy over. All that will copy over in source mode is strictly text. You must use WYSIWYG mode for copying over "extra" content, but that is as easy as switching the editor mode, then going back to source mode to edit.
Doing the edits above will put all reply, new thread, visitor message boxes default in source mode.