A larger front bead will effectively visually raise the front of your rib and make your gun shoot lower. This obviously isn't the same as changing the rib, but it might fool the eye enough to give you a feel for the adjustment. I've also seen people use balsa wood strips on ribs. They Magic Marker them black and just tape them on. It's good enough for an experiment though not for anything permanent.
Trap is a vertical game.
Skeet, particularly shootoff doubles where the game is really played these days, is mostly a horizontal game. Also, trap shooters usually use two different guns for three quite different games, so doing what ever is necessary to get a similar sight picture, while dealing with different points of impact, is at a premium. Many skeet shooters use only one gun and the game is always the same. If they do use a second gun, it will be an auto 12. For a skeet shooter it might be a little easier to get used to a certain sight picture that your gun demands, rather than modifying your gun for a certain sight picture that you demand.