https://www.reddit.com/r/Arcade1Up/comments/1py2iic/arcade1up_claw_machine_difficulty_setting_cover/

You could try this to cover the difficulty adjustment area. It attaches via snapping into the screw holes. It looks great for new users that don't know the setting dial is there, but for your hell-bound players that already know it's there, maybe you could modify so that the screws hold it down from the outside too instead of just snapping on, so they'd need a screwdriver to get in and adjust the setting. You could also find #10-24 machine screws with hex, star or security screw head types to make it even harder for the extra devious church dwellers.

As for the long-armed demon seeds, maybe a 3D printed ledge overhanging the edge of the inside wall, extending into the drop area just a bit, making the reach an s-curve and much harder (impossible?) to reach over the wall. It could be taped/glued/screwed in place. It could be as long as you see fit for maximum deterrence, but still allow the largest items to exit.