Keep iCloud contents but separate iTunes purchases
I have been using one Apple ID for purchases of iTunes apps, music, books on 5 Macs and AppleTV movies and using the same Apple ID for iCloud so that my Mac and iOS devices can sync. The purchased apps need frequent Update and need the password of the Apple ID every time they update. But the same Apple ID and password can access to my emails, calendars, notes and so forth.
I know I can use one Apple ID for iCloud and another Apple ID for iTunes purchases, if I start to do so at the beginning!
I know the purchased apps, musics, books and movies cannot be transferred to another Apple ID account due to DRM problem.
How can I retain all contents and move them to another iCloud account (a new Apple ID) that I am going to create?
MacBook Pro (13-inch Early 2011), OS X Mountain Lion (10.8.2), 8GB 1333 MHz DDR3