Earlier I was on Jenkins version 1.653 and the below script was able to set a parameter value from groovy post build script.
_def pa = new ParametersAction([new StringParameterValue("TestStatusLog", "Test Passed with Warnings")])
// add variable to current job
Thread.currentThread().executable.addAction(pa)_

Yesterday(7/18), I have upgraded Jenkins to version 2.13 and to my surprise, the above code is not working any more. Please check and try to fix this.