@esp@the.monsterpit.net Here's that minecraft mod we were talking about yesterday--configuring it is kind of complicated though so if you want I can make a config file since we've done it before and know how it works (and yes, though the feature isn't mentioned in the mod anywhere, this does work on chunks that have already been generated, not just when generating new ones)
https://www.curseforge.com/minecraft/mc-mods/wg-block-replacer
-F