Why am I unable to alter the Entry Type for a Message Base?
Message Bases, Oracle Service Cloud
The Entry Type is chosen when a message base is created. Once it is saved, the Entity Type can no longer be modified due to the framework specified for each of these Entry Types (plain, HTML, hot key attributes).
For additional information, refer to the Create a Custom Message Base Entry section in online documentation for the version your site is currently running. To access Oracle Service Cloud manuals and documentation online, refer to the Documentation for Oracle Service Cloud Products.