Hi @hbroccoli,
Thanks for the post.
To customize the acf WYSIWYG settings, you will need to hook into either the wysiwyg_tinymce_settings filter or the wysiwyg_quicktags_settings filter.
For more info on adding custom JS to fields, please refer to this topic: https://www.advancedcustomfields.com/resources/adding-custom-javascript-fields/