Yes, you can change the owner of any post on Discourse. To change the owner of a topic, you just need to change the owner of the first post in the topic.
To do this, first select the post:
Then click the ‘change ownership’ button:
Those pages are displayed differently than most Discourse topics. By default, the topics are created in your Staff category, but they are not viewed by users from within that category. When users visit your Terms of Service and Privacy pages, they will not see the system user displayed as the author of the content.