I recently changed my relationship status to "Separated" unlike other statuses, this one does not automatically publish to my newsfeed. Is there a way for me to publish this change?
This indicates that you have set this to not publish. You will need edit your privacy settings and allow Facebook to share this information.
I would imagine that if you want to publish your Relationship status change then you will have to set it back before changing your privacy settings.
Once you have amended your privacy settings then update your Relationship Status to "separated" and it should publish this to your wall.
How you control who can see your Relationship Status has now been moved.