C'est possible en copiant le code suivant dans le fichier _public.php de ton thème :

#Bricoland code for category and posts templates according to cat_id

$core->url->register('category','category','^category/(.+)$',array('myURLHandlers','category'));
$core->url->register('post','post','^post/(.+)$',array('myURLHandlers','post'));
$core->url->register('preview','preview','^preview/(.+)$',array('myURLHandlers','preview'));

class myURLHandlers extends dcUrlHandlers
{
	public static function category($args)
	{
		$_ctx =& $GLOBALS['_ctx'];
		$core =& $GLOBALS['core'];
		
		$n = self::getPageNumber($args);
		
		if ($args == '' && !$n) {
			self::p404();
		}
		
		$params['cat_url'] = $args;
		$params['post_type'] = 'post';
		
		$_ctx->categories = $core->blog->getCategories($params);
		
		if ($_ctx->categories->isEmpty()) {
			self::p404();
		} else {
			if ($n) {
				$GLOBALS['_page_number'] = $n;
			}
			$tpl = 'category-'.$_ctx->categories->cat_id.'.html';
			if (!$core->tpl->getFilePath($tpl)) {
				$tpl = 'category.html';
			}
			self::serveDocument($tpl);
			exit;
		}
	}
	
	public static function post($args)
	{
		if ($args == '') {
			self::p404();
		}
		
		$_ctx =& $GLOBALS['_ctx'];
		$core =& $GLOBALS['core'];
		
		$core->blog->withoutPassword(false);
		
		$params = new ArrayObject();
		$params['post_url'] = $args;
		
		$_ctx->posts = $core->blog->getPosts($params);
		
		$_ctx->comment_preview = new ArrayObject();
		$_ctx->comment_preview['content'] = '';
		$_ctx->comment_preview['rawcontent'] = '';
		$_ctx->comment_preview['name'] = '';
		$_ctx->comment_preview['mail'] = '';
		$_ctx->comment_preview['site'] = '';
		$_ctx->comment_preview['preview'] = false;
		$_ctx->comment_preview['remember'] = false;
		
		$core->blog->withoutPassword(true);
		
		
		if ($_ctx->posts->isEmpty())
		{
			# No entry
			self::p404();
		}
		
		$post_id = $_ctx->posts->post_id;
		$post_password = $_ctx->posts->post_password;
		
		# Password protected entry
		if ($post_password != '')
		{
			# Get passwords cookie
			if (isset($_COOKIE['dc_passwd'])) {
				$pwd_cookie = unserialize($_COOKIE['dc_passwd']);
			} else {
				$pwd_cookie = array();
			}
			
			# Check for match
			if ((!empty($_POST['password']) && $_POST['password'] == $post_password)
			|| (isset($pwd_cookie[$post_id]) && $pwd_cookie[$post_id] == $post_password))
			{
				$pwd_cookie[$post_id] = $post_password;
				setcookie('dc_passwd',serialize($pwd_cookie),0,'/');
			}
			else
			{
				self::serveDocument('password-form.html','text/html',false);
				exit;
			}
		}
		
		$post_comment =
			isset($_POST['c_name']) && isset($_POST['c_mail']) &&
			isset($_POST['c_site']) && isset($_POST['c_content']) &&
			$_ctx->posts->commentsActive();
		
		# Posting a comment
		if ($post_comment)
		{
			# Spam trap
			if (!empty($_POST['f_mail'])) {
				http::head(412,'Precondition Failed');
				header('Content-Type: text/plain');
				echo "So Long, and Thanks For All the Fish";
				exit;
			}
			
			$name = $_POST['c_name'];
			$mail = $_POST['c_mail'];
			$site = $_POST['c_site'];
			$content = $_POST['c_content'];
			$preview = !empty($_POST['preview']);
			
			if ($content != '')
			{
				if ($core->blog->settings->wiki_comments) {
					$core->initWikiComment();
				} else {
					$core->initWikiSimpleComment();
				}
				$content = $core->wikiTransform($content);
				$content = $core->HTMLfilter($content);
			}
			
			$_ctx->comment_preview['content'] = $content;
			$_ctx->comment_preview['rawcontent'] = $_POST['c_content'];
			$_ctx->comment_preview['name'] = $name;
			$_ctx->comment_preview['mail'] = $mail;
			$_ctx->comment_preview['site'] = $site;
			
			if ($preview)
			{
				$_ctx->comment_preview['preview'] = true;
			}
			else
			{
				# Post the comment
				$cur = $core->con->openCursor($core->prefix.'comment');
				$cur->comment_author = $name;
				$cur->comment_site = html::clean($site);
				$cur->comment_email = html::clean($mail);
				$cur->comment_content = $content;
				$cur->post_id = $_ctx->posts->post_id;
				$cur->comment_status = $core->blog->settings->comments_pub ? 1 : -1;
				$cur->comment_ip = http::realIP();
				
				$redir = $_ctx->posts->getURL();
				$redir .= strpos($redir,'?') !== false ? '&' : '?';
				
				try
				{
					if (!text::isEmail($cur->comment_email)) {
						throw new Exception(__('You must provide a valid email address.'));
					}

					# --BEHAVIOR-- publicBeforeCommentCreate
					$core->callBehavior('publicBeforeCommentCreate',$cur);
					if ($cur->post_id) {					
						$comment_id = $core->blog->addComment($cur);
					
						# --BEHAVIOR-- publicAfterCommentCreate
						$core->callBehavior('publicAfterCommentCreate',$cur,$comment_id);
					}
					
					if ($cur->comment_status == 1) {
						$redir_arg = 'pub=1';
					} else {
						$redir_arg = 'pub=0';
					}
					
					header('Location: '.$redir.$redir_arg);
					exit;
				}
				catch (Exception $e)
				{
					$_ctx->form_error = $e->getMessage();
					$_ctx->form_error;
				}
			}
		}
		
		# The entry
		$tpl = 'post.html';
		if ($_ctx->posts->cat_id) {
			$alt_tpl = 'post-cat-'.strtolower($_ctx->posts->cat_id).'.html';
			if ($core->tpl->getFilePath($alt_tpl)) {
				$tpl = $alt_tpl;
			}
		}
		self::serveDocument($tpl);
		exit;
	}
	
	public static function preview($args)
	{
		$core = $GLOBALS['core'];
		if (!preg_match('#^(.+?)/([0-9a-z]{40})/(.+?)$#',$args,$m)) {
			self::p404();
		}
		$user_id = $m[1];
		$user_key = $m[2];
		$post_url = $m[3];
		if (!$core->auth->checkUser($user_id,null,$user_key)) {
			self::p404();
		}
		
		self::post($post_url);
		exit;
	}
}

Ensuite, il faut copier le fichier category.html et le nommer category-x.html où x est l'identifiant de la catégorie. Ça marche aussi pour post-x.html.

Dans ces fichiers, tu peux traiter ensuite la catégorie (ou le billet appartenant à la catégorie) comme tu le souhaites