I think your first code was not so bad but you used keyexist to test if a value exist.
If the test on key is enough, use the code below :
 Code:
$key = "HKCU\Software\Work\Config"

If not KeyExist($key)
	$rc = WriteValue($key, "IncludeSubjectLabel", "0", "REG_DWORD")
	$rc = WriteValue($key, "IncludeSubjectLabelOnBrowse", "0", "REG_DWORD")
EndIf

if you want to make configuration if value doesn't exist, use glenn's code
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Christophe