Depending on how "complex" your message is, it would likely be much easier to either use the "Announcement" and just fill it out on that specific node (although, this will will inherit down to child nodes if there are any) or use the built in "Custom Content" fields which can be included like a custom component within a quilt, e.g.
<component id="common.widget.custom-content" name="<custom-content-id>" panel="false" />
if there is not already a node specific custom quilt, you then would just create that custom quilt for the node where you want to display the custom content, add (properly configured) the above code and override the default quilt.