As Iranian , I must say, you are so naive if you think people who holds the power in Iran genuinely believe in something. They are professional politicians. They know what are they doing, and they don't give fuck about Islam. Just search and look how they treated with traditional religious people in Iran (religious people who believes power and religion should be separate).
Actually this new generation of politicians (I mean Khomeini and after him) they are pretty good in changing old rules when they realize they are in losing side of the battle and not changing that rule will hurt they public figure in long run. Let me give you an instance, there is fuck load of hadith about chess itself being dirtier than alcohol (which punishment for it is death they catch you drunk 3 time), which in my opinion pretty absurd, like rest of religious beliefs. But Khomeini realized people will ask in long run what is dirty about chess ? And because it is so obvious that it is absurd, they changed the rule around 25 years ago.
My point is there is distance between something like hijab, alcohol, betting and something like chess. The idiots (mullahs) can justify (and they are aware of this fact) hijab for simple ordinary rural people (which is their only base in country other than people who earn money from this corrupt regime), but they cannot justify that even for naive people in rural area what is wrong about chess.
lets be honest, they don't give fuck about some bunch -not all of them, really small portion, I say it from my experience, right now I am student in Iran and I do regularly visit many universities in country- of student in university who shout and fight back for their rights, they would suppress them like lollipop if they try really hurt regime in any serious manner. If pressure become serious they would drop hijab rule in a day.
They may show to you they are 100% firm about their beliefs, but believe me when they realize just 1% danger (serious threat to regime nature, they don't give fuck about some chess championship tournament, what would happen? Tournament will cancel ? I bet the actual power in Iran would even be more happy if tournament gets cancelled), they would change their most basic rule if they can find a way to justify themselves to their supporters.