"Legally, this does more than merely mention the exception."

Suppose a constitution says:

"Freedom of speech shall not be restricted, except in situations X."

There are three different descriptions:

A. Mention

The Constitution mentions situation X.

This merely says the words appear in the text.

It tells us nothing about the legal effect.

B. Establish

The Constitution establishes an exception for situation X.

This means the Constitution itself creates that legal rule.

C. Permit

The Constitution permits restriction in situation X.

This describes the legal consequence of the established exception.

So:

mention = refers to it in words.

establish = creates the legal rule.

permit = describes what becomes legally allowed because that rule exists.

For legal writing, establishes an exception is usually the most precise wording.