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.
For me though, I believe that casinos does have such power or right to modify their terms and conditions, and not inform their users about it, only if they have specifically and categorically made it clear in their terms and conditions that, they have a right to modify the terms and conditions without prior or aftermath notice to their users, and also make it clear to their users that its is their responsibility to periodically go through the terms and conditions to stay updated with latest and unannounced changes.
I believe with such a line as the above included in the terms and conditions, users who read it and still go ahead to agree to it are doing or did so at their own peril, because personally, i legitimate casino with no interior or scam motives will not include such a line, but must make sure to announce to their users when their terms and conditions is going to be updated, or notify their users when they have modified their terms and conditions, i mean it cost nothing to do so aside sending out a couple of buck emails.
Some terms and conditions can be very elongated to the extent that you might keep getting yourself confused if care is not taken.
This is why it is very important for us to use simple casinos that will not stressed us with a lot of articles to read and comprehend.
There are some casinos that doesn't send updates on terms and conditions to customers, most time it is done selectively especially by dubious casinos using that to make some gamblers to lose big funds since they are not aware of the new update.