What is the difference between this mod and the already existing RePainter?

The main difference probably is how it runs.
Other map update mods I've seen work during on_tick, this mod runs entirely in a migration script. It runs a bit faster, but uses more memory since chunks can only be unloaded at the end of a tick and all migrations happen within the same tick.

Apart from that the other mods didn't remove and respawn trees, decoratives and cliffs to match changed biomes.

And what about ores? some of them reset those (like Regenerate Terrain) some don't.

I'm not touching resources nor biter.

So it would be safe to assume that running yours and repainter on a map would create the same result (technically, ignoring decoratives), just that the implementation is different? He mentions the end result would be bigger (the map size). Is this also the case here?

Finally, one thing that always irked me about repainter was the fact that it runs at every map load when it's enabled, essentially forcing you to keep it disabled/uninstalled if you didn't want to run it every time a map loads. Now, given your implementation i'm guessing it's besides the scope of your mod to add a button to trigger this regeneration on demand instead of all the time?

Tiles should be the same, but it'll look weird having lush green trees in deserts.

That's why I made this run as migration script. It runs only once per save. To run this again you'd have to disable the mod, save ,enable again.

Oh, interesting, then i guess yours wins a spot in my mod list :) Thank you for the info.