In order to edit a file, choose Open for Editing... from the File menu and select the file you want to edit. A registry editing window will appear which allows you to edit your registration file in the same way you edit the registry.

You will be presented a new registry window with the contents of the file. Certain functionality,  like bookmarks and undo will not be available in this editor.
When your are finished editing, choose Save from the File menu.

Opening a Registry Image for Editing

Registrar allows you to edit binary registry images on disk such as a registry backup, a registry hive file or a Windows system file which makes up the registry of a Windows installation. This feature allows you to edit and repair a registry configuration on disk which is damaged and would otherwise have remained non-bootable. To open a registry image for editing, select  Open for Editing... from the main menu and select files of type RegEdt32 compatible hive files in the file type selection box. Now browse to the registry image on disk you would like to edit and select it. Registry hive files which make up the systems registry are usually located in the %systemroot%\system32\config directory.  A registry editing window will come up which allows you to change the contents of the file. Note that when editing registry hive files, also registry security information such as permissions, auditing and ownership will be saved along with the file.

For more information on differences between different registry file formats, read Differences between Registry File Formats

 When you open a registry file for editing, Registrar needs some temporary storage space to prepare the editing window and process the file for editing. The keys generated for this purpose are volatile which means that they will automatically get deleted as soon as you reboot your system.

When opening a registry file for editing on Windows NT or 2000, make sure that you have enough registry quota available. In the case your registry size limit is too small, you may receive an error message. Change your registry size limit to a bigger value which leaves space for editing larger registration files.