How To Prevent Changing Theme in Windows 7
Changing a Theme in Windows 7 is very easy. Just right-click on desktop and select “Personalize”. Select the desired theme from the list and Windows will automatically apply it. Any one who has access to your Computer can do this easily.
You may not want your kid to play around and frequently change the theme. You can apply your favorite theme and lock it by following the steps below:
1. Logon to Windows 7 with Administrator rights.
2. Type gpedit.msc in the Start menu search box.
3. This will launch Local Group Policy Editor. In the left panel propagate to User Configuration –> Administrative Templates –> Control Panel –>Personalization

4. In the right panel, select “Prevent changing theme” and double-click it.
5. In the following “Prevent changing theme” window, select Enabled radio button.

6. Click Apply then OK. Now changing themes will be disabled.
You can check it by going to the Personalization screen. All the themes will be grayed out and a message “One or more of the settings on this page has been disabled by the system administrator”.
Tips:
Windows 7 also has some hidden regional themes which you can unlock and start using.

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