I bet that they could encode into the printer something that would stop a design from being printed that even closely resembles a gun.
Sure, and then you could just print the barrel separately from the magazine, receiver, trigger, grip, etc. So they’d have to try to stop you from printing anything that looks like even a part of a gun. Even then, it would be mere weeks before some hacker came up with a way around it.
And I bet a twelve year old “prodigy” could disable those limitations in less than a month.
How? The quintessential American “gun” is the AR15, which is legally defined (thanks to legislators not knowing what they’re doing) as the “lower receiver” part - a component of odd shape not resembling what most would consider a “gun”. Screw on other parts that also don’t look like one, and suddenly you have one.
There is no innate “signature” to such an object which fulfills the sociopolitical demand you indicate. Should a library of culprits be encoded, akin to the list of forbidden guns in the defunct-for-good-reason “assault weapon ban”, ‘tis not hard to make alterations until something passes muster.
This isn’t like photocopiers which detect & refuse to copy highly standardized images such as money. There is no identifying distinctive standard shape beyond a long hollow tube - and long hollow tubes have many legitimate purposes.