I worked on an HP3000 in the early 90s. It had a software package that changed all of the error messages to resemble IBM360 error messages, just to throw would be attackers off.
Was that package really intended to be a security feature? To me that seems like a low effort way of landing a contract with an over-specific requirement. But security practices used to be way different so that explanation is also plausible.
It was one feature of a security package. I honestly don't recall the name. I should clarify that I'm talking about error messages one might see during login. Not system-wide/post-login error messages. Looked like an IBM login but got you into an HP.
What? Was this something on the CSL (Contributed Software Library)? Don't recall anything like that...
Besides... I'd expect something emulating S/3x.
You could alter the system message catalog however you liked... Sounds like something that would happen to Whitman College's system :)
If no one could use the OS it wouldn't have survived longer than UNIX, and still be the option to go for high security deployments in some specific workloads.
I'm joking, of course. You CAN use MCP, if you need to. It won't be a pleasant experience, however. It can sense your fear.