Mass-Enable Commenting on CCK-Built Content-Types

Here's an SQL query you can perform in phpMyAdmin (or other database administration tool) to mass enable comments on all the individual nodes of a specified content-type.

UPDATE `node` SET `comment` = '2' WHERE `type` = 'YOUR-CONTENT-TYPE-NAME'

To disable comments, use:
UPDATE `node` SET `comment` = '0' WHERE `type` = 'YOUR-CONTENT-TYPE-NAME'