title: How to update a JSON value?
body: <p>I'm trying to use the JSON features of Delphi 10.3 but I can't get my around UPDATING a value in a JSON Object.
  AddPair creates a NEW pair, even if the name already exists and I find no way to set the value as all functions/properties are read-only...</p>
  
  <p>Do I really have to delete the pair and create it?</p>