You did not back-up the Registry and you can not make changes to one of the Registry keys because you do not have permission even though you are logged in as an Administrator and you have started Regedit with Administrator priveledges.
WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.
Once you make Permission changes to one the Registry keys and it is not the setting or permission that you want you try to change it back and it does not allow you to stating that you do not have permissions.
You need to run a Task using the System account that will overwrite any changes you may have done in the Registry as an Administrator.
For our example we want to delete the "configuration" key: [HKEY_CURRENT_CONFIG\System\CurrentControlSet\SERVICES\configuration]
* Right-click on the Key that you are having permission issues with and select Export.
* Save the file to c:\temp as a .reg file - our example we will save it as C:\temp\2bdeleted.reg
* open up the .reg file with a text editor and insert a dash before "HKEY_CURRENT..." and resave the file
1. Open up the Computer Manager console by typing "compmgmt.msc " in the Run window
2. Under System Tools click on Task Scheduler then on the right-hand side click on Create Task...
3. On the General tab create a name for your Task - Change User or Group... to System - also check "Run with highest priveledges" at the bottom
4. On the Trigger tab you can set the time that you would like the New Task to start but for this example we will run it once we complete creating the New Task
5. On the Actions tab click on New... and type in the following:
Regedit.exe as the program and the c:\temp folder where your 2bdeleted.reg file resides
6. There is no need to make changes to the Conditions and Settings tab
7. Once completed go back to the Task Scheduler and underneath select Task Scheduler Library
8. Right click on the Task that you named in Step 3 and select Run - this will result in the deletion of the "configuration" key
You can add a timed event by going to the Trigger tab.