Inserting new events and Updating metrics for existing events

Hello everyone,
I am currently working on a POC for using Druid to store advertising time series data of the form :
{“date”:“2017-11-18”,“campaign_id”:251250128,“adgroup_id”:13890648608,“term_id”:55630821488,“match_type”:“e”,“term”:“Crossbody Bags Simple”,“device”:“c”,“clicks”:0,“impressionss”:1,“total_cost”:0}

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The questions I need to answer are following:

  1. The event metrics can change certain days after the event occurred and has already been ingested into Druid. How do update event metrics in Druid using Segment Re-Indexing? The updated data would have to be read from a json file. I have read the information given here (http://druid.io/docs/latest/ingestion/update-existing-data.html) but it is not very clear to me.

  2. New events come in every day and need to be ingested. How do I create an index task to append new data to existing data in a Druid datasource?