It can't be forbidden since the FA decided no action needed to be taken after the apology and the case dismissed. Actually I think they (and UEFA) were (would be) terrified they would need to become involved at all since this is a massive can of worms. Look at Barca now saying PSG should have their feet roasted, talk about being hypocritical ! It wasn't Liverpool were 'incompetent' per se, it was a single individual at the club who got over-excited - excruciatingly stupid but an individual nonetheless.
It most definitely is. A manager cannot meet with another club's player without permission. Liverpool apologised and withdrew interest in the player, and it was on this basis that Southampton and the Premier League accepted that they would not pursue the matter further. Thus, if that interest is reignited, the premise on which Liverpool were not punished becomes defunct. That is why I am struggling to see how Liverpool can now be allowed to sign van Dijk.