Any regulated, law-compliant casino would not be able to pull any nasty tricks on their players via changes to ToS, as the law would usually offer protection to the players, or at least their deposited funds.
And for non-regulated ones, operating from exotic jurisdictions, regular studying of their ToS is probably pointless, as they could either change them whenever they see fit, or even ignore their own rules, as you unlikely will ever be able to take any legal actions, so it's all about trust and reputation.
As far as I know casinos have to ask users to agree with terms and conditions once again every time they make changes on it, doesn't matter how little they are, just like banks and every other services do. Moreover, a timeframe must be presented for users to cashout their funds, if they disagree the new terms. If casinos attempt to change (to forge) a document which was signed by an user, they are commiting a crime and will have to pay for it if the user denounces them to regulators.
However, proof is needed and I think the only way to do this would be to download and backup a copy of the terms and conditions on the moment of the agreement.
I think casinos are way wiser than that, they generally have a statement in their terms and conditions which says that they have the right to change, remove or modify any rule or statement written in terms and conditions at any given time, and guess what? Users agree with that when they are signing up, and when users accepted that themselves, there is nothing left about it and it wouldn't be considered a crime, it might be unethical not informing the customers though.
This is the reason why a gambler should always read the terms and conditions before they join a platform and they should always keep themselves updated. Most casinos don't make changes and if they do, they let their players know, but some might do it, so gamblers need to watch out.