How to override Tibco BW Global Variables in runtime

com.tibco.xml.xdata.xpath.Variable v = com.tibco.pe.core.Engine.getDeployedVarsVariable("DEFAULT_PROJECT");
com.tibco.xml.datamodel.XiNode gvNode =
com.tibco.xml.datamodel.XiParserFactory.newInstance().parse(new org.xml.sax.InputSource( new StringReader(vars) ));
java.lang.reflect.Field f = v.getClass().getDeclaredField("mValue");
f.setAccessible(true);
f.set(v, gvNode);