Look at what you are modifying before you modify it. That will help you determine these little, but extremely important, details.
Don't make a whole group of changes to the Registry at one time. Make only one change. Close the Registry. Observe the change. Often, for the change to take effect you have to refresh the desktop (click on an icon and press F5) or reboot the system. Just make sure the desired change took effect and that your system is working properly before making another change.
If everything is working fine, you might want to attempt another change. If you do, be sure to once again make a patch and, after editing the Registry, close it and take the necessary steps to be certain that all is working properly. After making several changes, you may want to back up the entire Registry again.