For newer machines you can quite often change percentage by loading the .gam file into notepad. Just right click on the gam file and open with notepad.
You will get something like this…..
System IMPACT
DIP 1 00000000
Delay 25000
Stake 4
Jackpot 4
Percentage 10
SetPercent 90
TotalIn 11790
TotalOut 10402
Played 36
Layout Snakes.dat
Sound SLaddersS.BIN
ROM SLadders1.hex
ROM SLadders2.hex
You change the number on percentage AND setpercent. For instance 80% is percentage 5 and setpercent is 80. 82% would be 6 and 82. 7 and 84 etc. Not sure how low it’ll go. Probably 1 and 72?