How to modify the xml on onRequestscript() in SOAP UI

Here is my code which i wrote in onRequestscript

def groovyUtils = new com.eviware.soapui.support.GroovyUtils(context)
    path = "D:\\Service\\something2.xml";
    log.info("path = "+ path);
    if (mockRequest.method == "POST" )
    {
 mockRunner.returnFile( mockRequest.httpResponse, new File(path))
 return new com.eviware.soapui.impl.wsdl.mock.WsdlMockResult(mockRequest)
    }

But this script changes my XML entirely... I want to modify an existing XML(something.xml)..

i was actually Not able to modify the xml so i thought of changinf the xml instead.But according to my business logic its wrong... So can any one help me to modify the xml
in onRequestscript....