Hi, I made some times ago.. so I don't remember well..
probably I did so:
I used S3D program (you find it here:
http://sh4.skwas.net/)
1. with S3D I opened stock and GWX's scene.dat
2. in left menù tree the Node39 was localized, and copied.
3. open GWX scene.dat
4. delete GWX's node 39 and replace it with the copied one.
5. save all.. and hope it might work!
IMPORTANT: always make a copy of your files that you are going to modify!!