Hello Prabhu,
you should have a look at the import/export functionality of the UME.
You can take one of the roles, that all these 200 users have, export it and you'll get a file. Now you change the name of the role to one of the new roles in the file (the file is build in a certain way, but you'll see) and then you can upload the file again and the system will update the users with the new role.
Don't forget to set the mark to overwrite the existing data (as you don't want to add new users, but change the users and their role assignments).
And then you can do the same with the second role.
You can test that with one user to get a feel for it, but it's a pretty simple solution. Look into the portal help for the UME and read through the export/import information and you should be good. 
Regards,
Steffi.
