I am trying to generate a world in minecraft with 4 times as much ore for my server, and I am doing this with the superflat world presets. I am using this website to generate the preset. The only problem, is that the preset is too large for the input field in minecraft (Find this field by going to Superflat>Customize>Presets). I tried removing all the quotation marks, and it still doesn't fit. I even tried using cheat engine to modify the memory values to have the whole string, but it never worked. Does anybody know how to do this? Is there another option to make the world generate 4 times as much ore?
Customised worlds were removed in 1.13. The "buffet" type is supposed to replace them in the future, but they don't have the feature you want yet.
Your best option is to generate a world in 1.12, go far out in all directions and then load it in a newer version. That way you won't get kelp, coral, turtles, etc., but many other resources can be obtained in other ways (sweet berries from chest loot, bamboo from fishing and panda spawns, …).