Override Comment Deadline

WordPress lets you set a number of days after which comments will be unavailable for individual posts. This plugin will allow you to keep commenting open on specific posts.

Once the plugin is enabled:

• Set a comment deadline in Settings > Discussion using the "Automatically Close Comments…" option. Closing comments on old posts is a great way to avoid spam comments.
• Edit an individual post on which you'd like to keep discussion open indefinitely and check the Override Comment Deadline box.