Updating template to include DocValue via api

I want to add DocValue to my default logstash-* template. I have seen documentation that says to add it to the raw section of the not_analyzed. But I don't have a config file on the server, so I will need to add this using the api. I haven't found any code for editing the index via a put statement, so I don't know the syntax to use. Can someone please share the syntax for updating a template? I am using this to view the template:

http://[eshostname]:smile: 9200/_template/logstash?pretty=true

The very first example in the index template documentation shows how to store an index template: https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-templates.html

Make sure you disable manage_template for your elasticsearch output.

So, do I just add a new index template? Or are you saying that if I use the same index name with the XPUT command (using the syntax from the first example) that it overwrite the existing template?

Yes, if the index template name in the URL matches an already existing index template it'll get overwritten by your PUT operation.

I was able to get my template updated, now I am wondering, how can I tell if docvalues are being applied to new indices. Is there a query I can run. Sorry if this a newbie question, but I can't find anything that shows how to tell if it is working or not. I want to make sure it is working correctly before I reindex the old data.