add note about mandatory messages

Author: mchammer01

content/admin/user-management/customizing-user-messages-for-your-enterprise.md

@@ -64,12 +64,21 @@ You can use Markdown to format your message. For more information, see "[About w
 {% if currentVersion ver_gt "enterprise-server@2.22" or currentVersion == "github-ae@latest" %}
 ### Creating a mandatory message
 
-You can create a mandatory message that {% data variables.product.product_name %} will show to all users the first time they sign in after you save the message. The message appears in a pop-up window that the user must dismiss before the user can use {% data variables.product.product_location %}. Mandatory messages have a variety of uses.
+You can create a mandatory message that {% data variables.product.product_name %} will show to all users the first time they sign in after you save the message. The message appears in a pop-up window that the user must dismiss before the user can use {% data variables.product.product_location %}. 
+
+Mandatory messages have a variety of uses.
 
 - Providing onboarding information for new employees
 - Telling users how to get help with {% data variables.product.product_location %}
 - Ensuring that all users read your terms of service for using {% data variables.product.product_location %}
 
+{% note %}
+
+**Note:** As mandatory messages are meant for use during the initial configuration of the system, you can only set up mandatory messages once. 
+
+{% endnote %}
+
+
 If you include Markdown checkboxes in the message, all checkboxes must be selected before the user can dismiss the message. For example, if you include your terms of service in the mandatory message, you can require that each user selects a checkbox to confirm the user has read the terms.
 
 Each time a user sees a mandatory message, an audit log event is created. The event includes the version of the message that the user saw. For more information see "[Audited actions](/admin/user-management/audited-actions)."