How to customize the LinkModal mockup pattern that is provided by TinyMCE

I am trying to customize the default Link modal that pops up on TinyMCE when attempting to hyperlink text. This refers to the Internal Link tab. The behavior that I want to add is having a dropdown with preset rootPaths to restrict the search to. This way users can quickly define up front which folder to search within. I know the tree provides it, but my use case wants a 1-click path for a number of preset folders that we know.

So first I set out to customize the Related Items pattern using this concept: https://training.plone.org/5/javascript/exercises/8.html#add-your-pattern-file

To extend: https://github.com/plone/mockup/blob/2.1.x/mockup/patterns/relateditems/pattern.js

The problem is that I do not necessarily want every interface that uses the pat-relateditems to implement the new behavior.

I also saw that I might want to extend the LinkModal pattern, but when I attempted to do that, I found that the extended version did not call the extended show function when the user taps to insert a link from TinyMCE.

require([
  'jquery',
  'tinymce',
  'mockup-patterns-tinymce-url/js/links',
  'pat-registry'
], function($, tinymce, LinkModal, registry) {
  'use strict';

  // first, unregister existing pattern
  delete registry.patterns.linkmodal;
  delete $.fn.patLinkmodal;

  // creating new pattern automatically registers it
  LinkModal.extend({
    name: 'linkmodal',
    trigger: '.pat-linkmodal',
    parser: 'mockup',
    init: function() {
      var that = this;
      LinkModal.prototype.init.call(that);
    },
    show: function() {
      var that = this;
      LinkModal.prototype.show.call(that);
      // customizations here
    }
  });

});

So my question is, does anybody have any good docs on how to customize the LinkModal?

Thank you in advance for any insights!

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