I successfully downgraded from 2.9.14 BETA back to 2.8.24
FTP to the radio
Upload all the 2.8.24 files to the router
Log off the FTP connection
Do Not reboot yet
Winbox into the router
Go to system package list
Highlight all 2.9.14 files
Delete the files
Reboot the router
All IP Addresses and Bridge Data were intact in my case
I had 2 wireless cards (Atheros) in my router
I did not see them in the interface window after reboot
I FTP'd back into the router and saw some files were still there (not yet loaded)
I rebooted the router from winbox and the files loaded.
Afterwards the wireless cards showed up in the interface window
I then needed to re-program both wireless interfaces
Be sure to check all your settings:
I found DHCP server settings I needed to remove
Also look for firewall settings
Then reboot the router again
Success!