Conditionally add action

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  onMouseEnter() {
	  console.log('mouseEnter', ...arguments);
    this.set('onMouseEnter', undefined);
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>

<p onmouseenter={{if onMouseEnter (action onMouseEnter)}}>
	Words!	Words!	Words!	Words!	Words!	Words!
</p>

{{#unless onMouseEnter}}
<p>
	onMouseEnter Removed
</p>
{{/unless}}

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-data": "3.4.2",
    "ember-composable-helpers": "2.3.1"
  }
}