He can demand a trade all he wants, he has no leverage. Which is why it would be a stupid thing to do.
Laughton got into Hextall's good graces by going back to the AHL and working hard on his deficiencies, and then taking those lessons back to Philly and embracing his fourth line role.
Once problem may be watching someone like Provorov get a major role at 19 and chafe at being asked to go back to the AHL instead of treating it like a wake up call. Even if Hextall doesn't like Morin and wants to trade him, he still wants the kid to force his way into the lineup and raise his trade value.
The reason Hextall doesn't put too much weight on preseason is simple, it's a few games, with adrenalin and rest, against inferior competition (young players and veterans gliding), where you can shine with talent. The regular season is higher intensity and a grind. Obviously, he didn't see what he wanted from Morin. Then Morin tried to hide his injury, which didn't make Hextall happy. But he was still ticketed for a 10 game tryout which would have given him a fair shot at showing he belonged. Opportunity knocks, you'd better answer.