What is LiveWorldgen?
LiveWorldgen is a dev tool specifically to only be used in development environments for people who are working on worldgen content such as features, custom noise settings, carvers, etc. and don't want to have to restart the game or reload in order to see how the settings affect the world.
This allows you to leverage your IDE's hot-reload functionality to instantly change the way things are being generated, and continue testing ingame without any further delay
How does it work?
Simply make a new class that extends LiveWorldgenAccess, instantiate it somewhere it will be accessed (at the top of your mod's constructor is an easy spot), then the mod will ask your instance to provide any values you want to override in realtime.
This allows you to provide new values on the fly, and see how they interact with the world.
Then whenever you make a change to any of the returning methods, reload changes in your IDE and it'll take effect immediately
Make sure you remove the class before building your mod, so that it doesn't go to production