Disable re-select when model was selected in Angularjs-chosen

I need help with the following scenario:

I use a single-select dropdowns in a table. Each row has its own dropdown.
Now there are 2 options for changing the selection:

  1. Click on deselect (‘x’) icon (works ok – via ng-change).

  2. Open the dropdown, choose another value from list. Override the previous value (although ng-change fires, I have no way to know if it’s a new value or a overriding value).

I wish to disable the second behavior. Is it possible to ‘tell’ chosen that once a value was selected, the only way to re-select a new value is to click on ‘x’?
e.g: once a value was selected, disable the dropdown, hide the ‘arrow’ icon, but keep the ‘x’ deselect icon active?

Thanks.

Source: AngularJS