Edited mesh changes back to old one once object is placed

I tried editing the cottage living animal barns but i'm assuming it's gonna be a lot more difficult than i hoped (again...). I edited the mesh and shadow LOD but once i place the object it turns back into the "old" barn.

Left is my new mesh before it's placed, right is what it turns into once i click!

Here's the file: www.simfileshare.net/download/2620876/

Pleaaaase don't tell me this will be a huge project again, i just wanted a simple thing for once :') Thank you in advance!