bitrix_body_class.php

<?php

function parseClasses($classes){
	return explode(' ', preg_replace('/[\t\s]+/',' ', trim($classes)));
}

function addBodyClass($class){
	global $APPLICATION;
	$classes = parseClasses($APPLICATION->GetPageProperty('body_class'));
	$add = parseClasses($class);
	$classes = array_merge($classes, $add);
	$classes = array_unique($classes);
	$APPLICATION->SetPageProperty('body_class', implode(' ', $classes));
}

function removeBodyClass($class){
	global $APPLICATION;
	$classes = parseClasses($APPLICATION->GetPageProperty('body_class'));
	$classes = array_unique($classes);
	$remove = parseClasses($class);
	foreach ($remove as $del) {
		if(($key = array_search($del, $classes)) !== false) {
			unset($classes[$key]);
		}
	}
	$APPLICATION->SetPageProperty('body_class', implode(' ', $classes));
}

Пример использования

addBodyClass('some-class petya elena vasya');
removeBodyClass('petya vasya');
echo $APPLICATION->GetPageProperty('body_class'); #some-class elena