If you have a problem with your system after running Registry First Aid corrections you can restore the initial registry state. Registry First Aid makes two types of registry backups: full registry backup made before the scan and backups of modified registry entries made just before modifying the registry.
You can restore the registry using the Start Menu -> Registry First Aid group -> Registry Restore shortcut. Or run Registry First Aid and click the Restore Backup link at the main window.
The Restoration Wizard will run and you will see two options: Restore the registry from .reg files or Full registry restore from system backup. See a screenshot.
If you found a problem with your system, first try to restore the most recent .reg backup file. Select the Restore the registry from .reg files option and click Next. You will see a list of available backups. See a screenshot.
After selecting backup items to restore, click the Restore button. It is suggested to restart Windows® to be sure that registry changes were applied. After reboot check if a problem still exists. If a problem persists you can then restore all of the .reg backup files created after the date you are sure the system was OK.
If none of .reg backup files solved the problem then you can restore the registry from a most recent system backup. Such backups are created by Registry First Aid on a daily basis before scanning the registry. I.e. if you scanned the registry twice yesterday then only one system backup was created.
This behaviour can be changed from the Select Registry Errors to Scan wizard page.
Run the Restoration Wizard from the Start Menu -> Registry First Aid group -> Registry restore shortcut and select the Full registry restore from system backup option. Follow the instructions.
Registry First Aid uses Windows® restoration tool to create full registry backups and restore. So, it is as safe as Microsoft can guarantee.
If a problem still exists after full registry restoration from a valid system backup then that problem caused by something other than Registry First Aid and doesn't deal with the program's registry correction.