How to read and update json messagein Groovy script via SoapUI NG pro

Satish, below script should provide you some direction. In this example, previous step is a REST Call and it uses it's response to use as a request for another REST. 

import com.eviware.soapui.support.XmlHolder
import com.eviware.soapui.support.types.StringToObjectMap
import net.sf.*
import net.sf.json.*
import net.sf.json.groovy.*
import groovy.json.JsonSlurper
import com.eviware.soapui.support.GroovyUtils
import groovy.json.JsonBuilder

//## Get previous test step name //
def currentStepInd = context.currentStepIndex
def TestStepName = testRunner.testCase.getTestStepAt(currentStepInd - 1).name  //Assuming REST request is your prior step

//## Parse json response ##
def response = context.expand( '${'+TestStepName+'#Response}' ).toString()
def json = new JsonSlurper().parseText response

//##Update JSON Nodes ##//
def jsonbuilder = new JsonBuilder(json)
jsonbuilder.content.status = 'Active' // Assuming 'Status' is one of json node

//## Build json body and write to a file as string ##//
def req = jsonbuilder.toString().replaceAll(~/\\n/,"\\n").replaceAll(~/\\r/,"\\r")  //escape char handler if needed

//##Update TestCase Property to contain parsed json ##//
testRunner.testCase.testSuite.setPropertyValue("JSONBODY", "${req}")

in the next REST step call this JSON  using  - ${#TestSuite#JSONBODY}

for Excel reading you could refer to below link-

http://www.techiethoughts.com/technical-posts/soap-ui/how-to-read-data-from-excel-sheet-and-store-it-in-an-array-list-to-process-them-using-groovy-script..html

if you store your JSON in a text file then you also use above like this

//## READ canned request from a file to modify ##//
def JSON = new File("C:\Requests\JsonBody.txt").text
def json= new JsonSlurper().parseText JSON 

Hope this helps!