Ember: How to rewrite/extend RESTAdapter to make it site wide?

If I extend adapter in app/adapters/application.js

let appAdapter = DS.RESTAdapter.extend({
  ajax: function(url, method, hash) {
    hash = hash || {};
    hash.crossDomain = true;
    hash.xhrFields = {
        withCredentials: true
    };
    return this._super(url, method, hash);
  },
});

export default appAdapter.reopen(config.adapterSettings);

it will still be superseded by model specific Adapters which I also have.

I have a few specific Adapters, for example: app/adapters/testpost.js

export default DS.RESTAdapter.extend(myTemplates, {
  myTemplate: `${host}/${dir}/testpost`,
});

For now to make it work, I extended each of them with the same piece of code, for example app/adapters/testpost.js became:

let testpostAdapter = DS.RESTAdapter.extend({
  ajax: function(url, method, hash) {
    hash = hash || {};
    hash.crossDomain = true;
    hash.xhrFields = { 
        withCredentials: true
    };
    return this._super(url, method, hash);
  },
});

export default testpostAdapter.extend(myTemplates, {
  myTemplate: `${host}/${dir}/testpost`,
});

The question: How to extend/rewrite RESTAdapter for all Ember, and for all specific adapters at once.

Tried to extend in app/app.js, doesn't work that way.