If a pair use a convention which is not permitted then the Director will give their opponents Ave+ and them Ave- and cancel the board. But he will let them finish the board first to see if the non-offenders get better than Ave+ in which case he will let the result stand.
Note that the term "licensed" was dropped five years ago because it was ambiguous. The EBU licenses tournaments and other things.
As to your other question it is difficult to be sure whether there is an infraction because of unauthorised information. If there is not then the players can do what they like.
However, it is unlikely to be permissible. If a player makes the wrong bid how does he remember? If because of his partner's alert or explanation then he must do everything possible not to take advantage of that alert or explanation, so he cannot try to get out of it.
If he does not have a problem with unauthorised information then he can do whatever he likes to recover from a mistake, and sometimes he will succeed.
To take a silly [but clear] case, consider your second sequece: 2NT - 3
. Now, if he has made an agreement to play 3
as a transfer to hearts [and I do know a pair who play that way] but he has forgotten then an alert from partner will not remind him, because a Stayman 3
is alertable. If he suddenly remembers he can try jumping to 5
and hope to get away with it, and perhaps he will.
But if an opponent asked what the 3
was and his partner's answer reminds him he may not use that information and he will get a score adjusted against him if he tries to recover illegally.