In reply to George Stephanis.

Thanks for the link George :) . But, I wonder if it affects the existing URL and permalinks to the post. For example, as mentioned above, I had created a parent category called 'Portfolio'. Under which I had other categories for specific genre of projects like 'multimedia' , portraits or weddings. I have this URL http://nishantratnakar.com/portfolio/multi-media/fistful-of-dreams/ - Now, if I switch the post type, wouldn't it affect the permalink? I am asking this because the wordpress.com documentation on portfolio gives a different permalink for portfolio projects with project slugs and project-type slugs.