Sed Lex

Add an update box in posts.
This box can contain a message, for instance in order to point out that the post have been modified of to stress that the post in no longer up to date
The message can be configured direcly when editing a post. There is a box ‘Update message’ added on the left.
In addition, you may use a shortcode [maj update=’dd/mm/yy’ expire=’dd/mm/yy’]xxx[/maj]
Plugin developped from the orginal plugin WP Update Message.
This plugin is under GPL licence.
<h4>Multisite – WordPress MU</h4>
This plugin works with multisite installation of WordPress.
<h4>Localization</h4>
<ul>
<li>German (Germany) translation provided by klotzi703611, RobertBergholz</li>
<li>Greek (Greece) translation provided by skyrodos</li>
<li>English (United States), default language</li>
<li>Spanish (Spain) translation provided by BrenardCrespo, notaspampeanas</li>
<li>French (France) translation provided by SedLex</li>
<li>Italian (Italy) translation provided by DarioDaniele, Androidous</li>
<li>Dutch (Netherlands) translation provided by MichaelWijnands</li>
<li>Polish (Poland) translation provided by Kajaczek</li>
<li>Portuguese (Portugal) translation provided by PedroNave</li>
<li>Russian (Russia) translation provided by MegaJeme, RobertBergholz</li>
<li>Turkish (Turkey) translation provided by kbasali</li>
<li>Chinese (People’s Republic of China) translation provided by wensonjo</li>
</ul>
<h4>Features of the framework</h4>
This plugin uses the SL framework. This framework eases the creation of new plugins by providing tools and frames (see dev-toolbox plugin for more info).
You may easily translate the text of the plugin and submit it to the developer, send a feedback, or choose the location of the plugin in the admin panel.
Have fun !

Update Message

Dreb Bitanghol

This field will provide you more options and flexibility on how you would like to present an instruction or message to your client’s (or site in general) admin interface.
Features:
<ul>
<li>Support PHP.</li>
<li>Option to hide label when field is displayed.</li>
</ul>
Compatible with Advanced Custom Fields:
<ul>
<li>4 (tested up to 4.4.6)</li>
<li>5 (PRO, tested up to 5.3.7)</li>
</ul>
PS: You need <a href="https://wordpress.org/plugins/advanced-custom-fields/" rel="ugc">Advanced Custom Fields</a> installed to use this.
PPS: Even more awesome if you have <a href="http://www.advancedcustomfields.com/pro/" rel="nofollow ugc">Advanced Custom Fields PRO</a> installed.
Important note: Use this with utmost care.

ACF Enhanced Message Field

Exactly what I needed

Exactly what I needed. You could improve the plugin by making the textarea field look more like an IDE, with system fonts, syntax highlights and so on.

Perfect

Awesome!!

Adds an enhanced version of the default Message field to accept PHP and certainly no wpauto().

Update Message vs ACF Enhanced Message Field