You need to clone your connection to set the value at runtime..
In the below example, replace SearchData with your Data Connection name.
var oCS = xfa.connectionSet.SearchData.clone(1);
oCS.soapAddress.value = "http://YourWebServiceURL?wsdl";
Thank you very much. I wasn't sure at first but it seems to work great and even fires the postExecute events (wired up directly in the XML source of the XDP) and retains all bindings.
I'm trying to use your suggestion but I don't see the CLONE after my data connection. Can you please suggest where I might be going wrong.