Changing of terms and conditions without notifying the users or gamblers is normal with online gambling websites?
No, it's not normal and not acceptable.
Any reputable casino or any other service provider must inform its users about any updates in their terms of service. They must also mention when the last time their terms were updated. Besides new terms and rules should not have a retroactive effect. Any company that doesn't do this does not respect its customers and it should be avoided at all costs.
They should notify you, but I’m sure they probably do. Some sites have newsletters they email out that you can opt out of. I think they probably don’t want to bother you every time they update their terms. I assume most of the time they’re doing it because they have to legally, not because they’re trying to target their own users.