Is it posible to send Tempo messages from within a process instance?...

May I ask about the business case?
Are you truly trying to post a message (as a specific users viewable to that person's followers)? Or will making a post as a user or system to a specific group meet the case? The system event and post as users are possible via smart services.

May I ask about the business case?
Are you truly trying to post a message (as a specific users viewable to that person's followers)? Or will making a post as a user or system to a specific group meet the case? The system event and post as users are possible via smart services.