Using the config below, I would expect the world-generator for the Overworld dimension to be DOOGLAMOO_S no matter which generator was selected when the world was created (I'm in Single Player). However, If I leave the world selection as "Default" when I create the world, I get the default generator for the overworld.

https://pastebin.com/qDSL5nNq

I fixed the issue trying to load DOOGLAMOO_S as a world generator, but now attempting to use DOOGLAMOO throws an execption.

Error: java.lang.ClassCastException: net.minecraft.world.biome.BiomeProviderSingle cannot be cast to com.dooglamoo.worlds.world.biome.BiomeProviderDooglamoo

This is a known bug in Doogmaloo and it looks like the author hasn't been attending to the mod in a while, so no option to fix it unless the code gets released to the public domain.

I'm going to close this isssue, but wanted to leave this note in case anyone else ran across this.