Is it possible to switch from one process template to other (MSF Agile to MSF Cmmi and viceversa..)

No it is not possible to switch the process template from one to another once the team project is created.


Because whenever the team project is created with CMMI or Agile process templates it will configure default classifications (areas and iterations), default security groups and permissions of the process elements, this will be been defined based on the selected process template.
If the users still wish to begin (Change) using the MSF Agile template or MSF CMMI template, my advice is to begin fresh, with a new project.