For now mod affects only newly generated chunks. Is it possible to add an option to cut an existing map? Assuming that user knows what he is doing/
Currently I try to make interesting map using "factorio-world" mod, and globe-like outline will be a nice touch, but there is kind of conflict. Factorio-world overrides any terrain generation to insert user image, and overrides even your mod settings. But base image is rectangular and I'm looking for some way to cut corners :)

that's out of scope for my mod

it looks like you could use this one, though: https://mods.factorio.com/mod/Delete-Chunk-Tool

Thanks for the answer!
"Delete chunk" leaves square pattern, which is not perfect
Though I found a way by editing source image and now Nauvis looks like this (just need to upscale a bit) https://imgur.com/a/eXesn6i
And other planets will be truly round thanks to your mod!