With this mod installed, I'm still unable to deconstruct the landfill that I put.
I tried with old and new (before and after I installed this mod) landfills!
It appears that this mod don't make any change in my game!
I leave 'Breakable landfill' enabled!
When I tested it it worked fine. But you need to break the landfill like any other tile e.g. concrete. So you just need to hold landfill or an other tile in your hand and deconstruct it that way.
Hope this helps.