On my grand Prix I changed the drops so you needed A and C or B and D.
On my surf Champ I made it so the skill shot (double bonus advance lane) doesn't reset to the far left every time, so you get to try to lounge for all five lanes depending.
On my Black Jack I made it so when you 'won' a hand the dealer's hand got higher, so you couldn't keep kitting the hole forever
A friend modded their Argosy so the spinner lit with double bonus instead of randomly