For the question to not get closed, it would need to be phrased in such a way that answers are not completely opinion based. These types of topics can easily fall into that category if not carefully worded.
Your example you used:
"How should a person undergoing gender reassignment be referred to? Should it be by their birth designation, their present status, or according to their preferred identity (or he, she, they)?"
would be an example of a primarily opinion-based question that should get closed because the answer depends entirely on a political opinion. In order to reword that question to not be primarily opinion-based, you'd need to preface it like so:
As someone who dissociates gender from biological sex and believes gender may be fluid, how would I refer to a person undergoing gender reassignment? Should it be by their birth designation, their present status, or according to their preferred identity (or he, she, they)?
By prefacing it with your assumptions, the question becomes more precise and excludes opposing opinions which would give radically different answers. You now target a single opinion (political view) and are exploring answers within that.