title: Is it possible to partially decode and update JSON? (go)
body: <p>I need to decode and update only a specific value of a json object. 
  The issue is that I don't know the full structure of the object. The encoding/json package  "ignores"/truncates the fields not provided in the struct so on encoding these fields are lost. 
    I'm wondering if it's possible to unmarshal only the structure I know, update it and then marshal it without to truncate/remove the unknown structure/information.</p>