Today I’m pleased to release a discussion-focused plugin to the directory, called Override Comment Deadline. Now you can have “Automatically Close Comments” enabled in your discussion settings to limit spam activity on old posts while keeping commenting open on specific posts. To use it, make sure you’ve set a deadline on the discussion settings page and then edit any post and check the box to keep comments open indefinitely.
You can download Override Comment Deadline from WordPress.org or install it from the Add New Plugins page in your admin starting today. If you have suggestions for changes, you can fork the plugin and submit pull requests with GitHub.