As of the time of writing this, the accepted answer to this by David Marshall answers the question, but doesn't provide any detail beyond the link itself. In the interest of writing an answer that is both easily readable and invulnerable to potential link rot, I decided to write my own answer to the question.
How do I update the Windows Registry using the command line?
reg command, made available from as far back as Windows Server 2000, is used for this exact purpose, and the syntax is fairly simple to use.
To add a key
Run the following in a command line window:
reg add HKLM\Software\Classes\MyKey
...where HKLM\Software\Classes\MyKey is the registry key that you want to create.
To add registry values and data along with keys, parameters are required. The
/v parameter specifies the name of the value to be added, the
/t parameter specifies the value type, and the
/d parameter specifies the data to be contained within the value.
To add the key
HKLM\Software\Classes\MyKey with a
DWORD value named
LegacyDisable that contains data of
reg add HKLM\Software\Classes\MyKey /v LegacyDisable /t reg_dword /d 000
To delete a key
reg delete HKLM\Software\Classes\MyKey
/v, for deleting a particular value within a key instead of the key itself;
/ve, to delete a key only if it contains no values; and
/f, which overrides the command's default behaviour of waiting for user confirmation and forces the deletion.
To delete a value within a key:
reg delete HKLM\Software\Classes\MyKey /v LegacyDisable
To compare two keys
compare also allows you to compare two registry keys, listing the differences between the two by default:
reg compare HKCR\.doc HKCR\.docx
To change the default behaviour of listing differences, and instead list both the differences and similarities between two different keys, use the
When adding or modifying a registry key that contains spaces, make sure to wrap the key in quotes to avoid a bad syntax error.
When referring to any of the registry hives in a key path -
HKEY_CURRENT_CONFIG - the
reg command allows referencing them using their abbreviated versions -
HKCC respectively - as demonstrated in the examples above.
When a command is about to overwrite a currently-existing value, CMD defaults to prompting for confirmation. To bypass this confirmation, use the
/f parameter to force the overwrite.
The linked Microsoft documentation for the
reg command doesn't list any supported operating systems after Windows 7, so it's currently unclear as to whether this command runs successfuly on either Windows 8 or 10. Input from anyone with these operating systems would be appreciated here.