Downgrade Synology DSM 5.0 to 4.3

What you’ll need:
DSM5.0-4482 (or newer is installed) for your particular DS.
DSM4.3-3827 for your particular DS.
Assistant Synology DS
A network and some cables.
A disk to be used for installation.
Your data, back up a safe place.
A DiskStation be downgraded.
Get the DSM versions here

1: Back up your data.
2: Clean the new installation disk of all data and partitions.
3: Remove the unit of data (you did back there?) And install the new drive.
4: Use Synology Assistant DS, DSM5.0 install on the new drive.
5: Leave the DiskStation to start up and get to the desktop.
6: In Control Panel> Terminal and SNMP, Telnet or SSH enabled, if you prefer.
7: Telnet (SSH) in the DiskStation. User / Pass is root / youradminpassword
8: Using VI to make these changes to the file /etc.defaults /VERSION.

vi /etc.defaults/VERSION

Install the latest version of 4.3, so the code below does DiskStation think that you are running the version directly before.

MajorVersion = "4"
minorversion = "3"
buildphase = "3"
BuildNumber = "3810"
smallfixnumber = "3"
builddate = "19/12/2013"

9: Save the file and exit VI and exit the terminal.
10: In DSM, select Control Panel> Update & Sync> Manual DSM Update. Choose the file you’ve already downloaded 4.3 to 3827. Do not check for updates, and do not install anything with studs.
11: Allow time for the installation and restart DiskStation. About 10-20 minutes will be sufficient, but may be longer depending on the machine.
12: Once this is done, you will get the login screen 4.3. DS Assistant should report running from 4.3 to 3827.