Flattening Bedrock in a World You Already Started

Installing the mod into an existing save does not automatically fix bedrock you have already generated. New chunks follow your config, but old chunks keep their original bedrock until you explicitly ask for retro-generation.

Understand the two switch types

Each dimension file has genTop/genBottom and retroGenTop/retroGenBottom. The gen pair applies when a chunk is generated for the first time. The retroGen pair applies to chunks that already exist. If you only set the gen switches, you will see flat bedrock at the edges of your explored area but jagged bedrock everywhere you have already been.

Enable retro-generation

Open the JSON file for the dimension you care about, for example the Overworld or Nether file, and set the matching retroGen switch to true. Set retroGenBottom for the floor and retroGenTop for a ceiling. Save the file.

Back up before you load

Retro-generation rewrites terrain in existing chunks, so make a copy of your world folder first. Then load the world and move through the affected areas so the chunks are loaded and processed. Bedrock should be replaced with the block named in fillBlock.

Watch for side effects

Any build that relied on the old bedrock shape, such as a portal frame sitting in the floor, may be affected. Check important builds after the change and turn the retro switches back off once you are satisfied.