elgg/mod/ckeditor/views/default/elgg/ckeditor/config.js  : this file controls many behavior of the CK Editor text box in Elgg. For example : if I remove 'Bold', 'Italic', 'Underline', I will no longer see the [B] [I] [U] buttons. 

define(function(require) {
require('elgg/init');
var elgg = require('elgg');
var $ = require('jquery');
return elgg.trigger_hook('config', 'ckeditor', {'editor': 'default'}, {
toolbar: [[ 'Strike', 'RemoveFormat'], ['NumberedList', 'BulletedList', 'Undo', 'Redo', 'Link', 'Unlink', 'Image', 'Blockquote', 'Paste', 'PasteFromWord', 'Maximize']],
removeButtons: 'Subscript,Superscript', // To have Underline back
allowedContent: true,
entities: false,
baseHref: elgg.get_site_url(),
extraPlugins: 'blockimagepaste',
defaultLanguage: 'en',
language: elgg.get_language(),
skin: 'moono-lisa',
contentsCss: elgg.get_simplecache_url('elgg/wysiwyg.css'),
disableNativeSpellChecker: false,
disableNativeTableHandles: false,
removeDialogTabs: 'image:advanced;image:Link;link:advanced;link:target',
customConfig: false, //no additional config.js
stylesSet: false, //no additional styles.js
});
});

Now I want to add config.enterMode = CKEDITOR.ENTER_BR;  so that ENTER on key-board gives lines that are broken with <br> elements instead of paragraphs. For some reason I need this. I am unable to put this code in the above file. Or where else can I configure this? Can someone please guide me exactly where in the above or elsewhere (and how) I can use config.enterMode = CKEDITOR.ENTER_BR;