Is it possible to download a map from the MARK V generator and edit it in the map editor?
Well, not strictly "download", but you can save if as soon as it loads in the game. You can then move that save into the editor to work on it.
You can find the save at:
%USERPROFILE%\Documents\My Games\creeperworld4\saves\colonies
Look for the folder with a number equal to the map number.
To put the map in the editor, create a new folder with then name that you want to use for the map in this path:
%USERPROFILE%\Documents\My Games\creeperworld4\editor
For further questions and a quicker turnaround, use our Discord.
NOTE: if you use Onedrive then the folders may be in a different location:
%OneDrive%\Documents\My Games\creeperworld4\saves\colonies
and
%OneDrive%\Documents\My Games\creeperworld4\editor