The getPrivacyLevels provides information that is independent of all individuals. It provides a mapping from the numeric privacy level numbers stored in the database to the privacy level names displayed on WikiTree pages. The privacy level names are describe on the Privacy page. Internal to the database, privacy levels are represented by numbers that correspond to these names. This issue reports that I found a number in the data I retrieved that does not have a corresponding name in the the data returned by the getPrivacyLevels action, but which does appear on the Privacy help page.
In general, the API does not allow you to change the live data shown on WikiTree pages, in fact, according to the documentation, the API reads from an almost-live copy of the live data. When you use the API, you can see anything the public can see when they visit WikiTree. When you login to the API with your WikiTree credentials, you can also see anything that you can see when you are logged on to WikiTree.
So, to address your concerns, the API enforces the same privacy restrictions that WikiTree enforces on web pages. A non-logged-in guest will see no private information, and the logged-in user will see only the pages that he is allowed to see on the WikiTree pages.