Hello, if you want an answer to your question, I have a method for this problem but I'm not using mods
I just go to the game version file in .minecraft--> versions and choose the one that you are currently playing, then open the jar file inside with winrar and go to data, minecraft, worldgen, structure set and then choose the structure you want to modify and open it (the text file) and follow these instructions: https://minecraft.fandom.com/wiki/Custom_world_generation/structure_set
I really hope it will help you, and it is also the same protocol for mods,
Have a nice day/night and sorry