We're already in PM contact
There is an unofficial/leaked version of NECFlash modified to perform a full dump, including the calibration data. It's used when crossflashing NEC/Optiarc drives (e.g. ND-3550 to 4550), so you won't find it here
Dumping has never been a problem and if required I can supply people with such a version
If it does a full dump from the drive, you might be able to edit the serial number then flash everything back to the drive. (Unless there is a checksum to block it.)
The full dump is nice to verify the current serial number. But we already switched to PLSCSI and a simple command that just dumps the memory containing the serial number
Alternatively, if you can do a full dump from the faulty drive, you could (in theory) replace its motherboard with one from a healthy ND-4570A and flash it with the dump from the faulty drive (no hex editing required).
This probably will not work as you would also overwrite calibration data on a full flash. I know the command that should overwrite the drive's serial number with a given value. If this doesn't work, I will need to investigate further
[EDIT]Also the serial number printed on the drive doesn't necessarily have to be the one that's used internally. In that case you first need to find the serial number that the drive reported before[/EDIT]