Drupal - Can you bulk enable comments?

I'd also recommend Views Bulk Operations. You could create a view with a filter of that content type and add enable comments as an action. Then it offers you to select all.

Quite the useful admin tool.

That will work; don't forget node_revision.

UPDATE NODE SET comment = 2 WHERE type = 'foo'
UPDATE node_revision SET comment = 2 WHERE nid IN (SELECT nid FROM node WHERE type = 'foo')