To expand on that:
let’s say that Avalon pays out 95% (I dont know what it really is), and let’s say MG wants it now to pay out 90%
In order to achieve that they would need to change the payout amounts for certain events. So currently 2 scatters pays 2x your overall stake. They could try changing that to 1x your overall stake. Then they would run a simulation, playing the slot machine millions or billions of times, and at the end they could calculate how much the overall payout had been affected by that change.
One final, simple, example:
You create a casino game called ‘Coin Flip’, where the player bets on a coin coming up heads or tails.
You design it so it pays evens if you get it right, and nothing if you get it wrong.
This game then has a 100% payout, because each event (heads/tails) will occur 50% of the time, and when it does occur you get paid back double your stake, and when it doesn’t occur you get nothing.
So how do you change this game so it pays out less than 100%? What you do not do is change the odds of heads/tails occuring! That is cheating, the casino cannot do that.
What they do is change how much gets paid for a win. So instead of paying evens, perhaps it pays 1:2 – i.e. if you bet $2, you win $1.
Now the game doesn’t payout 100% any more, because you altered the rules to give a different payout. You did not alter the RNG or tell the software to give out heads/tails more or less frequently.
That’s how casino games work – hope that’s clear.