Unfortunately removing the assets does not accomplish the goal. The access to the line is 'hard coded', for lack of a better term, meaning with or without the object being draw you still won't have access.
Here a little playground I've got going to help you visualize what I'm talking about. Its built using MonoGame framework.
And it's 4:40 am...woo
Edit:
I got bored this evening so reworked my project a bit. Should have enough functionality to remove the trees and patch the access issues afterwords.
If you care to get my project running you can pull up a cruddy winform by pressing "O". This will show you a list of all the terrain objects on the map. If you select a row it will tint the corresponding object red. You can edit all of the properties from the datagrid and it'll update real time in the main window.
You may notice there are no objects drawn when you first open it...don't ask why I still have the default of false but simply press "t" and, viola, map objects will be drawn.
Wanna see accessibility? Press "g". Change the accessibility? While grid is shown left or right click.
It is pretty messy and horribly written, but as far as I know its the best publicly available/open source map editor.
Again, I'm up at ~4am so obviously not a professional/good programmer so I'm not entirely sure what it'll take for anyone to run this. It's using monogame, thats all I got for ya.