i don't want people to edit raw html in the tinyMCE WYSIWYG, can the html edit button be removed?

also, how to add advanced function buttons not already present?

you can disable html edit function from tinyMCE easily to modify code on story.inc.php files.

go to function tinymce_form and
delete option "code" from theme_advanced_buttons1 parameter. it will not show HTML edit code.