The same casino script is being used on other webistes such as nanogames.
It once was available to buy, same as with the Stake/Primedice casino script.
I don't think they are able to change the outcome since you can verify each round for yourself and set your own custom seed.
I don't think script is what op is talking about, op is talking about the algorithm of of a game namely, coin flip.. Except there be something I am not understanding clearly..
Game algo is not the same as the script the casino built on, and even at that I believe script can still be updated by any casino if they deem it fit, this could be to make the casino look a bit unique from other casinos using that same script..
Algo clearly differs, which is why we see different casinos offering or showing different RTP for the same game.