At the risk of seeming like I'm on a soapbox, I'll answer your question. If your son has had a change of heart, then no, they should not release him. That is my opinion. If the coaching staff has changed, or there is some problem on the school's end, then it might be appropriate to ask for his release. If he wants his release so that he can go to a different program, I would hope the school stickes to their guns and doesn't let him out of his signed commitment to attend that school.
You should realize that college coaches job security depends on having a stable program that wins its share of games. By signing and then losing prospects, they've also lost out on the opportunity to get someone else who may have contributed to their program had your son not committed, but who is now playing for a different college. Players backing out of signed NLI commitments is a significant problem for the college program, and should not be taken lightly at all. I counsel every player in my organization that if they have even the slightest doubt about their ability to live up to even a verbal commitment, to not make a commitment at all. Once they've signed, then I tell them that unless the coaching staff changes or there is some problem that is very significant, then they have no legitimate reason to back out. Of course, there are a few exceptions like family tragedies and illnesses, but that stuff doesn't enter into 99% of the times these things happen.
If he wants out of his commitment bad enough, he can go to jr. college for a year or two and then see if anyone wants him after that. Personally, as a coach, I have a very dim view of any player who doesn't live up to his commitment.
You asked, I hope that answer doesn't hurt too much.