I have seen issue when the updated request is going to LIVE system with lisa_vse_request.setBody(mySubTree);
The property "lisa.vse.http.current.transaction" holds the current transaction information in VS and lisa.vse.http.current.transaction.body" holds the request payload.
To change the VSE request payload, need to capture it first and modify that with the desired value and then set the new payload in the current transaction.
In the VSM, this can be done in an "Execute Script" step or in a "Scripted Assertion" with the below Bean shell code
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import com.itko.lisa.vse.http.HTTPTransaction;
import com.itko.lisa.vse.http.Transaction;
String OriginalRequestBody = testExec.getStateValue("lisa.vse.http.current.transaction.body");
String MofifiedRequestBody = OriginalRequestBody.replace("Original Text to be replaced","Replacement Text");
HTTPTransaction transaction = ((HTTPTransaction) testExec.getStateObject("lisa.vse.http.current.transaction"));
transaction.setPayload(MofifiedRequestBody);
return testExec.getStateValue("lisa.vse.http.current.transaction");
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Support created a knowledge article and it is available at https://comm.support.ca.com/kb/how-to-update-vse-request-and-send-it-to-live-system/KB000127510
Hope this helps.
-Prema