I'm assuming that it is just the setup/status/diagnostics control panel so you'll not be able to print anything arbitrary (shame, it could be a fun game!). If you are of a mind to wind someone up you might be able to kick out a pile of test pages and reconfigure the thing so it is no use until someone does a factory reset.

A similar but worse case was some years ago when a range of consumer router+firewall boxes had a fault which made them present their control interface on the WAN interface and had no password set by default. A large number of those somehow got into a search index (it may have also been Google, I can't rightly remember), and from there you can probably do more harm than you can from a printer.