Input:

{
  "PartyStatus" : {
    "item" : [ {
      "RleStsVal" : {
        "prtyRleStsVal" : "0001",
        "prtyRleStsTyp" : "Active"
      },
      "RleStgCd" : {
        "PrtyRleStgTp" : "0002",
        "PrtyRleStgDesc" : "Prospect"
      }
    } ]
  },
  "MaskedFlg" : false
  
}

Expected Output:

{
  "PartyStatus" : {
    "item" : [ {
      "RleStsVal" : {
        "prtyRleStsVal" : "0001",
        "prtyRleStsTyp" : "Active"
      },
      "RleStgCd" : {
        "PrtyRleStgTp" : "0002",
        "PrtyRleStgDesc" : "Prospect"
      },
      "key" : {
        "sourceKey" : "",
        "rowid":""
      },
      "$original": {
          "RleStgCd": {},
        "RleStsVal":{}
        }
    } ],
    "$original": {
      "item": [
        {
          "rowid": ""
        }
      ]
    }
  },
  "MaskedFlg" : false,
   "$original": {
     "MaskedFlg":true
   }
}

for the input json, have to add $original object which contains all the keys available at that level. for the array have to add one more object sourcekey along with dollar original