Is there a way to register for updates on certain NTSB investigations? I would like to track the progress of an investigation of a particular accident, NTSB WPR18FA200.

Some areas of the FAA website (advisory circulars, for example) allow users to register to receive updates by email when these items change.  Is there a similar functionality available for users of the NTSB accident database?  If so, where do I find it?
No, the NTSB does not have such a service on their web site. In theory you could track the progress by downloading their database and parsing it to determine if status has changed, or by figuring out how their query system can be invoked, but those options require programming skills.