Resolved gh-341 that adds the feature to expand the custom field option far beyond the default. Moved the menu prefix option in to the Joomla component area -> tab -> Settings to allow each component to override the global setting.

admin/compiler/joomla_3/JFormFieldCustom.php

@@ -0,0 +1,35 @@
+<?php
+/**
+ * @package    Joomla.Component.Builder
+ *
+ * @created    30th April, 2015
+ * @author     Llewellyn van der Merwe <http://www.joomlacomponentbuilder.com>
+ * @github     Joomla Component Builder <https://github.com/vdm-io/Joomla-Component-Builder>
+ * @copyright  Copyright (C) 2015 - 2018 Vast Development Method. All rights reserved.
+ * @license    GNU General Public License version 2 or later; see LICENSE.txt
+ */
+
+// No direct access to this file
+defined('_JEXEC') or die('Restricted access');
+?>
+###BOM###
+
+// No direct access to this file
+defined('_JEXEC') or die('Restricted access');
+
+// import the list field type
+jimport('joomla.form.helper');
+JFormHelper::loadFieldClass('###JFORM_extends###');
+
+/**
+ * ###Type### Form Field class for the ###Component### component
+ */
+class JFormField###Type### extends JFormField###JFORM_EXTENDS###
+{
+	/**
+	 * The ###type### field type.
+	 *
+	 * @var		string
+	 */
+	public $type = '###type###';###JFORM_TYPE_PHP###
+}

admin/compiler/joomla_3/settings.json

@@ -400,6 +400,11 @@
 					"rename": "layoutmetadata",
 					"type": "layoutmetadata"
 				},
+				"JFormFieldCustom.php": {
+					"path": "c0mp0n3nt/admin/models/fields",
+					"rename": "JFormFieldCustom",
+					"type": "fieldcustom"
+				},
 				"JFormFieldList.php": {
 					"path": "c0mp0n3nt/admin/models/fields",
 					"rename": "JFormFieldList",