Once enabled these themes will always be available to you.There are two ways to enable these hidden themes.I will explain both of them to you and you can use any one of them whichever you find easy.
Here is the step by step tutorial with screenshots on how to Enable/Unlock Hidden Themes In Windows 7
Method 1:-1.Goto Control Panel.
2.Click on Folder Options.
Note:- If Folder options is not available ,change the view to large icons at top-right corner of the screen
3.Now Click On the View tab.
4.Now uncheck the box Hide protected operating system files (Recommended).
5.It will show you a warning.Click Yes.
6.Now Goto C:\Windows\Globalization\MCT\
7.Inside this folder you will see folders with name MCT-XX where XX will be AU,CA etc.These are the country codes in which these themes are automatically available.
8.Inside each MCT-XX you will see a Theme folder.Open it and click on the .theme file to unlock it.
9.Once unlocked the theme will be available to you in personalization option.
METHOD 2:- This is a simple method as compared to the above method
2.Copy and Paste the following code into it.
Windows Registry Editor Version 5.00
3.Save it with the name allregional.reg
4.Now double click on it.It will ask for your permission to add the file to registry.Click on Yes.
5.Right click on desktop and select personolize.You new themes will be available to you.