Yes you can! At the top of the People Page, there is a dropdown menu called "Actions." From this menu, you can download CSVs of your Active people, your Unsubscribed people, or the whole kit and caboodle with the "Download Everyone" option.
There is a fourth option: "Deactivate everyone." This will allow you to move everyone to your "inactive" list: if someone is on the inactive list, that means they won't be surveyed in the future until you move them back to "Active" by re-importing them via CSV or by manually doing so on the People page in AskNicely.