Custom User Agent for HttpClient?

How about

    HttpClient client = new HttpClient();
    client.DefaultRequestHeaders.Add("User-Agent", "my-user-agent-name");

var client = new HttpClient();
client.DefaultRequestHeaders.UserAgent.ParseAdd("MyAgent/1.0");

There is also a TryParseAdd if you want to catch bad attempts at adding it and Add if you want to create the ProductInfoHeaderValue with a name and version number yourself.

Here you go

var client = new HttpClient();
client.DefaultRequestHeaders.Add("User-Agent",
                                 "Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.2; 
                                  WOW64; Trident/6.0)");