Can we configure the default message send for default email notifications per ta

Harish - this should be a good place to start : forum.appian.com/.../Configuring_Notifications

Certain XML files will need to be updated/created and appropriately referred, on the server to make this work.

To answer specific to your query, from the process designing end, I believe this can't be achieved. Changes to the server side configurations, affect all the users.

Thank you.