I did a downgrade of my N299, so it's possible.
You have to backup all your data, because you have to make a factory reset and delete all the partitions on the harddisks of your NAS.
That's what I have done:
1. backup all data on the N299 to my computer.
2. make a factory reset and restart NAS
3. after the N299 is up again, i powered it off.
4. removed the disks and installed them in my computer
5. deleted all the Partitions on my 2 NAS disks
6. removed the disks from computer and installed in the N299 again.
7. setup N299, made the RAID configuration and installed firmware 1.00.26
Now, I'm running fw 1.00.26 again, because I was much happier with this release than with newer beta versions, before the downgrade, I had 1.00.37.
I hope, that this short guide could help someone to successfully downgrade his N299.
But, you will do it at your own risk, i will not be responsibly for any damage.
Best Regards,