The plugin blocks all posts by default and leaves pages unblocked.
With a little tweaking, this can be changed (as djenkins mentioned). The function wpmem_securify is where the plugin determines whether to block or not. There are basically three possibilities:
- it's a post (is_single)
- it's a page but not members-area (is_page() && !is_page('members-area'))
- it's the members-area page (is_page('members-area'))
This function as it is written goes through a series of conditions to determine whether or not to block the post. For the first two points above, one of those conditional statements looks for a custom field as follows:
- Posts: (!get_post_custom_values('unblock'))
- Pages: (get_post_custom_values('block'))
Making a slight tweak to these changes the defaults. If, as you mentioned, you wanted posts to be unblocked by default but wanted to leave open the possibility to block at your will, then change the condition of posts from:
Now posts will be unblocked, but if you wanted a specific post to be blocked, you would set a custom field of "block" to a value of true (or 1, either should work) for that post.
Hope that helps!