Add some fields to events before storing them to tracker stores

I want to add some fields to the events before saving them to the tracker stores such as

    "sender_id": "user_id",  # instead of default id
    "timestamp": 1528402837.617099,
    "event": "bot",
    "text": "what your bot said",
    "data": "some data"

Is there any way ? If yes, can you provide me some example to modify it. Thank you.