I think game providers only provides the casino with games but the domain name must come from the casino themselves and I think I already saw a kind of domain they are talkin there. I think it is only normal, so I'm not bothered with that.
As for the slot replays, I think the providers name is mostly starring here. Right that a site can also use alternative domains to bypass restrictions or for some users to access them immediately because the main domain can be traffic. Some casino has their own original game, so they can change the RTP's on them in a legal way but licensed operators can still look for other factors and see if they are qualified or not.
The game providers only give the end user a URL, which should be iframed. That is how it normally works. As for the original games, any regulated operator that is licensed is required to undergo extensive code reviews when making any changes related to game logic. It is not normal for an operator to simply change the RTP of a slot via a dropdown as he provides it, and no regulatory authority would approve such a system. Like I said, if you do not care about regulations, go ahead, but even then, players will notice that these are not the real games. Cracked slots often not only have a lower RTP but also feel different because the people who cracked them do not have access to the backend logic for the reels, so they have to write their own logic, which will never be the same as that of the real provider.