Will manually setting the expire timestamp in the boost_cache table actually expire the cache for a node? I am trying to get myself acquainted with Boost running on my Drupal 6 website. I know that boost has a boost_cache table where it stores the expires value for each node. 

Now I want to know whether that if I set the value in the expire column manually to a preferred value, Boost will recognize it and expire the cached version of the node on the date in the timestamp and there is no other table related to Boost caching where I should make the changes.
You might prefer to use

boost_expire_node

which will actively flush the node from boost static html cache

It could be scheduled, if needed ( e.g a hook_cron_queue_info implementation worker callback ) or done as an immediate expiry