Admin-->Tools-->Define Pages
You can set the wysiwyg in Configure-->Define Pages
once you're done editing the pages back them up into your template folder with the same path.
They are php files not html files. but you can use html to edit them. Just be sure you save them as php.
they are in /includes/language/english/html_includes/
Make a template folder /includes/language/english/html_includes/templatename
replace templatename with the name of the template your using and copy the files into that folder AFTER you edit them.
The override system doesn't account for these pages.