FOSS gamedev and creative worlds

Hi, I want much more grass. Is there a mod or can I tweak some mapgen settings?

I know this mod. But I just want more grass on "dirt with grass" nodes and maybe dry grass on "dirt with dry grass"

Ok, dryplants does nearly what I want. Had to tweak a little bit

You could write a mod (that has default in depends.txt) that has 'minetest.clear_registered_decorations' then copy and paste all the decoration definitions from default/mapgen.lua, then change what you want.
Adjust the numbers here (except the 1-5 third number): https://github.com/minetest/minetest_game/blob/master/mods/default/mapgen.lua#L1307