How can I Bypass restricted HTTPWebRequest Headers

I've made a little helper function to deal with my HTTP requests that simply takes a string URL and a string array of headers formatted as Header-Name: Value

public static HttpWebResponse MakeHttpRequest(string URL, string[] Headers)
{
    HttpWebRequest req = (HttpWebRequest)WebRequest.Create(URL);
    req.Headers.Clear();
    foreach (string h in Headers)
    {
        var s = h.Split(new char[] { ':' }, 2);
        req.Headers.Set(s[0], s[1]);
    }
    return (HttpWebResponse)req.GetResponse();
}

But if the Headers array contains a Restricted header (e.g User-Agent, or Content-Type, or Accept, etc..) I get an exception telling me to modify the header using its property or method, so I was thinking maybe there was some way to check if any of the Headers was restricted and automatically modify it using its property, unfortunately, I'm not too smart so I don't really know how to do that without having a lot of bloated code checking every single restricted header and having different code run for each one Im guessing it can be done with Reflection but I'm not sure... Help?