Last updated: 20210509
Download and run https://github.com/dezem/SAK
Select “NSZ to NSP”
Set the original NSZ files to unlock read-only.
Select “Open NSZ” and find/select the .NSZ file for converting. It takes about 3 minutes per 1GB of conversion. So if your game is 10GB, it will take up to 30 minutes.
PS: You will not see any progress bar, just “please wait” flashing. That’s normal.
Once complete, your will find your .NSP converted files in the SAME FOLDER where “SAK.exe” is at. Strange.. but that’s that.
Now install your game using the converted .NSP file.