Excellent question. I know, for example, if by copying you are referring to (my logical thinking) of show configuration in clish, what you could do is something like this. On your existing gateway, run this from expert -> clish -c "show configuration" > /var/log/currentconfig.txt
That will save file called currentconfig.txt in /var/log directory. Once you get that file off the appliance, on your new box, just copy it over to same or different directory and then go to clish and run -> load configuration /var/log/currentconfig.txt
That will load the config or at least try, depending where config does not match and it would give failure. Then you just need to modify the file and run the command again.
Hope that helps. Apologies if you were referring to something else all together.
Andy