If you want to mangle HTTP requests you are better of with tools like Paros or the Burp Suite. Have a look at the OWASP page for further info. However, if you would like to send them manually with telnet you can use the template below.
Warning! This template worked for me, you should adjust it for your case.
GET /myfile.php HTTP/1.1 Host:myhost.com User-Agent: Mozilla/5.0 (compatible; MSIE 8.2; Windows NT 6.0; en-US) Accept: */* Accept-Language: en-us,en;q=0.5 Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Cookie: mycookie=12345 Referer: http://localhost.com/
I created a small python script, http-py, available on Github do the manually queries.