Not directly. You can do it with access to the instance's Postgres database, but I'd expect relatively few instance admins (as opposed to instance owners) to have that; the admin tools don't include a database console, and you can't use a credential for the admin tools to authenticate to the database.
If you are the instance owner you can do whatever you want. Additionally, many instances are installed on a single host (https://masto.host) and almost all instances are on VPS in various managed clouds.