Templates can be shared across multiple sub-accounts. This makes it possible to access the same template from different sub-accounts by different users.
In order to share a message, first you need to save it as a template.
Only account administrators have access to templates. Read more about user permissions.
Save your message as a template. Use the "Save as template" option from the message editor.
Share this template with any or all sub-accounts. Sharing is available under the "Configure" tab of the template editor. Ensure the template is "Published" to make it discoverable in other accounts.
The template is now available from any account you shared it with. Click the "Create new" button from the list of messages page to use it.
Learn more about template settings.