I hope in the next version of MT there will finally be a more straightforward way to disable the auto-conversion of dirt to dirt_with_grass and cobble to mossycobble on a world-by-world basis, possibly via a setting in minetest.conf for backwards compatibility. Right now it seems the only way to override this behavior is by hard-coding the changes in default/functions.lua, which is a far from ideal solution.
These ABMs in particular grief maps that were created in older versions of Minetest where such behavior didn't exist by default. Just reading through the feature request on GitHub, it is clear that this change was implemented primarily because developers thought it would be cool, rather than considering its implications for existing builds.