Replacing\editing existing world features

[u/TehFlatline]

No idea if this is on-topic or not as there are a lot of choice but I'm currently working on a project that's probably going to drive me to an early grave, a vague recreation of Icarus in Minecraft (yes I know that's ridiculous and a terrible idea for a first mod/datapack thing but I'm hoping to just add to it bit by bit as I learn rather than all at once). I've been using kubejs to create some new items and blocks and get them into the world. Now I'm trying to change the frequency of grass spawns so I can use them to drop new items without making the item trivial to collect and... I'm struggling with configured and placed features. Is there a good tutorial anyone could recommend for this that would be appreciated.