How to replace complete object within JSON Object in Sql server

I am trying to modify existing json in sql and adding a new property in each object in array.

My json is as given below

{"Key":"Employee", "Data":[{"id": "1", "value": "Vogel"},{ "id": "2", "value": "Vogel"}]

Now I am trying to add a new property in each object inside Data property(Like IsDeleted :False).

Can we iterate each object inside a particular property which is an array in itself and add property in each object.

One possible approach is to convert $.Data part of your JSON string to table with OPENJSON(), SELECT rows with new isDeleted column as JSON and modify original JSON:

DECLARE @json nvarchar(max)
SET @json = N'
    {
    "Key": "Employee", 
    "Data": [
        {"id": "1", "value": "Vogel"},
        {"id": "2", "value": "Vogel"}
    ]
    }';

SELECT @json = JSON_MODIFY(
   @json,
   '$.Data',
   (
   SELECT items.[id], items.[value], 'False' AS [isDeleted]
   FROM OPENJSON(JSON_QUERY(@json, '$.Data')) 
   WITH (
      [id] nvarchar(10),
      [value] nvarchar(100)  
   ) AS items
   FOR JSON PATH
   )
)   

Output:

{
    "Key": "Employee", 
    "Data": [{"id":"1","value":"Vogel","isDeleted":"False"},{"id":"2","value":"Vogel","isDeleted":"False"}]
}