A class you can drop-in to enable readonly text fields that can't be changed, but optionally you can set `'can_edit_capability' => 'manage_options'` to any capability you'd like to restrict editing to. If user has that capability, a basic text field will be used.

class-fieldmanager-readonly.php

<?php
/**
 * Read only text field, optionally allows for specific users to edit
 * @package Fieldmanager
 */
class Fieldmanager_ReadOnly extends Fieldmanager_TextField {

	/**
	 * The capability a user must have to be able to edit normally
	 *
	 * @var string
	 */
	public $can_edit_capability;

	/**
	 * {@inheritdoc}
	 */
	public function form_element( $value = NULL ) {

		// Allow specific users to edit
		if ( $this->can_user_edit() ) {
			return parent::form_element( $value );
		}

		return '<code>' . esc_html( $value ) . '</code>';

	}

	/**
	 * {@inheritdoc}
	 */
	public function presave( $value = NULL, $current_value = array() ) {

		// Allow specific users to edit
		if ( $this->can_user_edit() ) {
			return parent::presave( $value, $current_value );
		}

		// Don't allow changing value
		return $current_value;

	}

	/**
	 * Whether the current user can edit this field
	 *
	 * @return bool
	 */
	public function can_user_edit() {

		if ( $this->can_edit_capability && is_user_logged_in() && current_user_can( $this->can_edit_capability ) ) {
			return true;
		}

		return false;

	}

}