Hi Holger,
The
code:configure radius mgmt-access [primary|secondary] shared-secret encrypted "(encrypted_secret)"
command will allow you to copy the config over to another switch and should work. In our lab, this is how I apply my RADIUS config to other switches. You won't be able to take the password in the config directly and enter it - you'll need to use the "encrypted" keyword to tell EXOS that you're giving it an already encrypted password.
If you knew the password, you would enter it directly without the "encrypted" keyword in the command. The switch would then encrypt it and safely store it in the config.
Here's some more information on the command:
http://documentation.extremenetworks.com/exos_commands/EXOS_All/EXOS_Commands_All/r_configure-radius...