If a casino takes ethical values into consideration, they would probably inform their users about the changes that they've made in the terms and conditions, but if they don't care about all that, they would obviously not make that happen and wouldn't inform their users at all.
In some cases, there is a regulation that enforces companies to inform users each any changes they have made. ToS is an agreement, it should be legally void if there significant modification without noticing the user. Actually, it came back to users' consumer protection laws in their own respective countries. If the regulations are enforced, the user should be aware and informed of such a condition.
There should be also limitations on what can companies do, surely they did not have the right to do "anything" they want freely without any legal basis.
Like some weeks back when stake updated their terms of service, they made sure no user entered their account without first reading the terms of service, but still, many people did not read it, they just scrolled down the page, clicked the "I have read and agree to the terms and conditions" (what ever way it's written) button and then move on with their normal gambling activities, several millions of people out there only read the terms of service of a platform when ever they have encountered or have issues with the platform..
What I think is that when a casino that is recognized and old updates its terms and conditions it is because it needs to quickly integrate into a new way of seeing games of chance , I am not sure if that includes Bonuses and Bonus terms that they are not so difficult , but a casino should make its update based on what is Coming for the future and may be better, not that it will predispose the position of the players, because with dissatisfied players the casino will not perform well and will have many losses and that is not only what is Sought , a casino must stand out very well According to its competition.