The casinos does not change the algorithm of the games, they just increase or decrease the RTP (Return to Player) for the games. So if the split was 96% to the player and 4% to the house.... then they just change it to $93 to the player and 7% to the house.

It might also be that for 3rd party games, that they might alter the variance of the games, which is one of the other factors that are used to determine the outcome of the bets. (Slots)

The bets are still Provably Fair, because the Client Seed / Server Seed and RNG has not changed.