Making changes to the terms and conditions of a casino wouldn’t cause for any big panic, they just need to make sure it reaches out to everyone that has opened an account with the casino, both past and existing customers. ToS is not something that changes periodically but keeping informed your customers is important to show how transparent you are to them in delivering your services and to also build trust between the parties.
Yes, TOS is not something that will change suddenly, and if it will change, they will notify you well in advance before the new TOS is enforced. For example, what happened to Stake at that time they required their users to do KYC, they didn't just do it as they pleased, but they gave a very long time and even routinely notified their users to do KYC and even gave prizes to users who did KYC within the time they had specified.
Most of the TOS at the casino are the same, but there are some slight differences and that's natural because they also have considerations for the terms they will use. And it's also true that this is one of the goals to make both parties trust each other.
Unfortunately most casinos do not inform players in advance when they want to change the terms, some casinos do not even notify players when there is a change or some changes on the terms. Even if some casinos notify their players about an update on their terms, usually the notification given is not specific because most casinos will only inform something like "we have just changed our terms" without mentioning which part is changed.