Hi all,
First to note that Silverstripe Recipes seems not updated with any code except CustomConfigHTMLEditorField. The is outdated and does not support the silverstripe 3.1. I tried to customize and could not do so. I need to stop after checking the script that needs replace behaviour.register method in old with entwine method.
CustomConfigHtmlEditorField

Has I need only the replacement of content editor I created newcms configuration and set the following

public function getCMSFields() {
		$fields = parent::getCMSFields();	
		$fields->removeFieldFromTab('Root.Main', 'Content');
		HtmlEditorConfig::set_active('newcms');
		$htmlEditorConfig = HtmlEditorConfig::get('newcms');;
		$fields->insertAfter(new HtmlEditorField('Content', _t('SiteTree.HTMLEDITORTITLE', "Content", 'HTML editor title')),'Description');

		return $fields;
}

Now this shows editor without the editor.css styles .

I have to add this to CMSFields to set the theme css file.

		$htmlEditorConfig = HtmlEditorConfig::get('newcss');	

		$cssFiles = array();
		$cssFiles[] = FRAMEWORK_ADMIN_DIR . '/css/editor.css';
		if(class_exists('SiteConfig') && ($config = SiteConfig::current_site_config()) && $config->Theme) {
			$theme = $config->Theme;
		} elseif(Config::inst()->get('SSViewer', 'theme')) {
			$theme = Config::inst()->get('SSViewer', 'theme');
		} else {
			$theme = false;
		}
		
		if($theme) $cssFiles[] = THEMES_DIR . "/{$theme}/css/editor.css";
		$htmlEditorConfig->setOption('content_css', implode(',', $cssFiles));

All because of Config::inst()->get('SSViewer', 'theme_enabled')
Where do I enable theme or disable it?