Underlying directions ... ?

We can distinguish two cases:

(1) We discover that we are following a tacit rule which we can articulate without substantially disrupting our present linguistic practices.

(2) We discover a similar rule, but its articulation would cause substantial semantic disruption.

The second is a bit puzzling - how can we 'discover' a rule without articulating it?  I think the answer is that we make an experiment, and it has a revolutionary effect on the language community.

We can resist rules of the second type by refusing to articulate them. But we cannot articulate the rule 'do not articulate rule X' without articulating rule X. We can see approaches to dealing with this in authoritarian institutions. Or so I think. And maybe I'm getting ahead of myself.

A signalling system cannot be semantically 'open' - it would just be ambiguous, or incomplete. A language must be semantically 'open' if it is to develop (even in response to what we think of as 'empirical' inputs).

Signalling systems don't need to develop in this way. They are semantically closed. Perhaps we say that they have a formal semantics - which is as much as to say they have an eliminable semantics. So maybe no semantics at all. Apart from their dependence on the semantics of the language in which they are formally described.

Why would the discovery of a tacit rule cause semantic disruption? A simple case is dogmatic truth: insistence on a literal fundamental truth is vulnerable to open question observations. (To ask why the dogma is true is to contemplate the conditions under which it might not be.)

A language which cannot contemplate some of its own tacit presuppositions also cannot articulate which of those presuppositions cannot be contemplated. It must depend on habit or fear rather than argument.

The 'safe' thing to do will be to avoid too  much ...