Apologies if this is either already known, or should be in the World Editor forum (that looked to be more for tips & sharing).
When I load a .world file with an ocean level not 0, the editor seems to ignore the value. If I immediately save the loaded file and look at the JSON, the ocean level in the file is 0. Thus, I need to remember to manually reset the ocean level every time I open the file in the editor.
In my case, I do this because the wave tips sometimes poke through my beach, and it's much easier to lower the ocean to -0.04m than to move hundreds of objects up by that much.