https://social.msdn.microsoft.com/Forums/vstudio/en-US/dde72fbe-e741-48fd-a9e1-253800d5227a/is-any-way-to-change-wcf-test-client-config?forum=wcf

Answer

The reason timeouts and MaxReceivedMessageSize can't be propagated to the generated client config is because that data is not propagated to the wsdl published by the service.  Only operation ports, and WS* standards are in metadata.  Further, MaxReceivedMessageSize on the service has nothing to do with MaxReceivedMessageSize on the client.  You can have a request-reply scenario where the request sent to the service is very small, but the service returns a large response.  In that scenario you MUST manually modify the MaxReceivedMessageSize on the client.  There's nothing in metadata about this.