There's a usual line related to terms and conditions, "some terms might be changed or modified without noticing users".
The casino does have the right to modify or add new terms and conditions without agreement with the user, but the new policy must not be detrimental to the user, the casino still acts fairly and is responsible for paying the jackpot withdrawal without making it difficult for any reason. We may not be able to do anything if the casino decides to unilaterally harm the user, but we have control to report the casino to the community by including valid evidence, the casino will lose its users because gamblers do not use casinos that harm users, without users gambling will not operate and slowly the casino will go bankrupt unless the casinos fix everything before the big trouble comes along.
It's true that casinos often update their rules without necessarily getting agreement from users. But it's good to know that any changes shouldn't put users at a disadvantage. The casino is expected to treat everyone fairly and, of course, when someone hits that jackpot, the withdrawal process should be smooth sailing.
Gladly on my own experience, when chagnes on my online casino I'm playing with, stakes, vbet" notifies users about their changes days before. So when having withdraws I have bit adjustment when I am directly affected with the updates of services.