Searching around I see this question has been posted multiple times with no resolution, but I think I have the answer!
Extract the nupkg file
Download the program dotPeek: dotPeek: Free .NET Decompiler & Assembly Browser by JetBrains
Use the program to open the dll file.
In it, you’ll see under “Resources” all the original xaml files. Save those back to the extracted folder where the “project.json” file is.