In the area where you select your island, there would be a button that said 'your islands'. Here you could either press 'create new' or decide to use an island you already made. In the islands, you could edit predator spawn rate, add tiles, add berry bushes and rocks, set climate, make hills, etc etc. I think this could add a lot to sandbox and make challenges -especially ones like the Warrior Cat challenges- so much more fun. I know it would be hard to add, but it would just be really cool in my opinion.