Right click on your Blockland shortcut on the desktop.
Click Properties.
Where it says target, after the last " add -mod editor
So it's something like this:
"stuff....\Blockland\Blockland.exe" -mod editor
Then while you're hosting, press F11, this opens the editor.
While editor is open:
F3 will switch to edit mode, which allows you to change values on objects.
F4 will switch to create mode, which allows you to browse through lists to spawn objects.
Note: In edit mode, if you delete an object, and try to expand/collapse a value group or apply settings, it will crash. Select a different object first.