Manipulate the text in the in-place editor

The args.newText value is read-only and you can change the text by canceling the default event and submitting the adjusted value:

dp.onEventEdit = function(args) {
  args.preventDefault();
  args.e.data.text = args.newText + " modified";
  dp.events.update(args.e);
};

Since version 2020.4.4730 the args.newText can be modified directly:

dp.onEventEdit = function(args) {
  args.newText = args.newText + " modified";
};

Please note that both approaches only work in onEventEdit. The onEventEdited method is fired after the default action.