I am trying to come up with such a solution that the user is going to enter the URL of a web-service and it is going to be tested.
Althogh what I want is a URL change, I guarantee the Service Description is always going to be the same (except the wsdl:service tag of course which contains the soap:address); I just want to test different customers, running the same service.
yes you can. just change the url property of the service proxy before calling any methods on it.
Yes; every web-service proxy offers a way to do this; with pre-WCF proxies (including WSEx) the address is the Url property on the proxy class - just change it before you do anything interesting with the proxy.
With WCF, I believe you specify the endpoint-address via one of the constructors.
So just generate your proxy from your reference wsdl, and off you go ;-p