That's right, you can reset ore generation height, vein size, and probability.
And you can get really picky, like ramping up only the redstone in a lava world or something, but I didn't have that long to tinker yesterday.
You can reset biome size, water size, water depth, and even choose a specific biome for your world. Mesas have been dreadfully hard to find, well, now you can pop one out in a variety of flavors.
You can choose whether or not to have mineshafts, dungeons, and other generated structures.
So you can pull up anything your heart desires in singleplayer now, and then reset the difficulty and mobs loading it into realms once you've settled into a game you want to keep.
Today is about doctor follow up on the atenolol taper and getting groceries. OH, and finding my USB sticks. I had a bad half hour yesterday realizing my life is so upside down now reshuffling my mobile office so many times without proper recovery and restructure that I couldn't find a single one when I really needed it, so my job today is getting my evil back on track.
