For the Advanced Generators mod by Bdew, he explains in the comments that you can add additional recipes to the various multiblocks through the use of datapacks, and he even links .json files from his github page as examples... but as someone with no datapack experience, I find it difficult trying to figure out how exactly i'm supposed to compile those into a datapack.
I've watched a tutorial explaining the basics of datapacks, and I was able to successfully make and load one into a world. But in what I watched, they give no indication how to interact with forge or mods within datapacks. I could imagine that's pretty vital to getting them to work properly.
If anyone has any good tutorials that may explain how to accomplish this, i'd greatly appreciate them. Or, if someone has a moment to explain in text how to go about it, that works fine too - I'm using VSC with the datapack addon, per the tutorial video's instruction.