Moderators and site administrators can change titles, and often will if they feel that an existing title misrepresents the content. As to the question in your

Moderators and site administrators can change titles, and often will if they feel that an existing title misrepresents the content. As to the question in your title: anybody on the same network as you. HN does not use a secure connection, so arbitrary people can listen for your session cookie and therefore impersonate you. This insecurity can be mitigated (but not eliminated) by using a VPN to a server on a more secure network