Manipulate json before send

Hello! I have to edit json structure before send. Is it Possible?
Here’s how I would need it:

{
"firstname": "name",
"lastname": "surname",
     "guesttypes": [
        {
            "Man": {
                "id": "12345",
                "quantity": "2"
            },
        }
       {
           "Woman": {
                "id": "12346",
                "quantity": "1"
            },
       }
    ]
}

Thanks in advance for support
Regards!