I recently got a PAMCO Contact (Master) and noticed that a previous owner had made an incision in the sliding under-plate that keeps the balls on the playfield, and which is pushed in to reset the game.
They had carved out the "OUT" hole at the bottom, so that while playing any ball that makes it to the bottom is returned to the shooter lane, just like in a bingo machine.
A nightmare for operators, sure, but in a home environment I found it actually makes the game even more. It let's you land all 10 balls into pockets. And for games with playfield advances via a trigger hole (like Contact, Signal, etc) it provides more action that way.
I don't see myself cutting out that hole in any other games, but I have decided to leave the Contact Master as-is and not fully patch up that bottom plate.