Присвоить id полю и подгрузить редактор с нужной настройкой в assets/plugins/tinymce/js/mce_init.js.inc.
tinyMCE.init({
theme : "advanced",
mode : "exact",
width : "305",
height : "120",
convert_urls : false,
document_base_url : "/",
language : "ru",
elements : "introtext",
plugins : "advimage,advlink,contextmenu,style",
file_browser_callback : '[+file_browser_callback+]',
external_link_list_url : "[+link_list+]",
theme_advanced_toolbar_location : "top",
theme_advanced_toolbar_align : "left",
theme_advanced_buttons0 : "",
theme_advanced_buttons1 : "bold,italic,underline,link,unlink,image,justifyleft,justifycenter,justifyright,justifyfull,removeformat,code",
theme_advanced_buttons2 : "",
theme_advanced_buttons3 : "",
theme_advanced_buttons4 : "",
verify_html : "true",
cleanup : "true",
cleanup_on_startup : "true"
});для id="introtext" например для Аннотаций.