2019-05-01 Page is work in progress, if you see any errors or have more information please let us know.
Generally when you edit your terrain you need to start a new career savegame, however you can bring over your old savegame vehicles and money etc stuff with a bit of file moving work.
Keeping the same savegame after terrain files updates: start new career, copy your OLD careerSavegame, economy, farmland and vehicles xml files over to the new savegame dir.
When you load up server with this savegame, the field states like crop growth stages are reset to their original values. So this is kind of cheaty way, you could harvest same field without ever seeding it, but why would you go through all that trouble for what you can do through dev console. Just keep it in mind that its best to reset savegame when you have harvested a field so there is no more work to be done.
If you have not edited heightmap dont copy over terrain.heightmap.png
If you have not edited ? dont copy over cultivator_density.gdm
If you have not edited foliage layers dont copy over fruit_density.gdm
weed_density.gdm hmm I dont think this is edited in GE, I have never edited it?