Read only in one group, posting in another
It's not a problem. It's the new spelljammer, actually, and the Helmsman can sense everywhere, so the characters would know it, anyhow.
But if I have to make a new character and transfer it between Helmsmen, it's just as easy (or difficult) to just transfer access to the Helm room list between Helmsmen, and leave them on the general list. And hope they remember not to post on the general list, which is going to be true either way, it seems.