I would also like to know how to edit the wysiwyg, but not only the toolbar!
what i know is:
because acf not use the default tinymce of wp-core (or at least use a own init method) some solutions that work with core didnt work with acf-wysiwyg fields.
Additional/similar Topics to this thread (with no answer!)
http://support.advancedcustomfields.com/forums/topic/wysiwyg-editor-acf-is-missing-general-wp-editor-functionality/
http://support.advancedcustomfields.com/forums/topic/acf-pro-wysiwyg-not-getting-changed-default-settings/
