[1.7.10] changing the overworld gen

I want to change the overworld totally. Which means I plan to create my own biomes and ONLY use these. Also I wanted to change the fillmaterial of the world, which is stone by default, to another block.

Right now I'm quite stuck doing this.

I managed to create my own biome and generate it in the overworld, but im stuck with removing the vanilla biomes and changing the fillmaterial.

I have no Idea how to change the fillmaterial.

For removing all biomes and use my own I tried the following.

Right now I am using only one biome to test it and registered it for every BiomeTyp, so none of the lists are empty because then it crashes for me.

(this is party of my load method)

BiomeManager.coolBiomes.clear();
BiomeManager.desertBiomes.clear();
BiomeManager.icyBiomes.clear();
BiomeManager.warmBiomes.clear();
BiomeManager.oceanBiomes.clear();

BiomeManager.addBiome(BiomeType.WARM, new BiomeManager.BiomeEntry(biomeWasteland, 100));
BiomeManager.addBiome(BiomeType.DESERT, new BiomeManager.BiomeEntry(biomeWasteland, 100));
BiomeManager.addBiome(BiomeType.COOL, new BiomeManager.BiomeEntry(biomeWasteland, 100));
BiomeManager.oceanBiomes.add(biomeWasteland);
BiomeManager.addBiome(BiomeType.ICY, new BiomeManager.BiomeEntry(biomeWasteland, 100));