Using fiddler to change the port of a request

Using fiddler to change the port of a request.
Look here for how to do it:
http://docs.telerik.com/fiddler/KnowledgeBase/FiddlerScript/ModifyRequestOrResponse

Here is how I did it, I put this in the fiddler script:

if (true && oSession.fullUrl.Contains("someUrlPath/thatNeedsNewPort"))
        {
            oSession.host="localhost:12300";
        }