> Bambu is patching a security issue.

This isn't a security fix. As a security protocol, it wouldn't pass any kind of security audit. A security fix would be something based on a per user credential, not on obscurity.

> Personally I don't want any device or application to send any old G-code to my printer.

Username/password over TLS would do that better than what Bambu Lab is proposing, as an extremely simplistic example.