Actually I would just copy and paste everything as normal first, and then run the "NO IP route" commands on whatever you needed to remove. A lot of the commands aren't going to duplicate, but commands like IP addresses you're allowed to have multiple of them, so that is why you'll end up with more than one. If you're telnet/SSH in and you run a no IP address before you assign the new one, you might be able to lock yourself out of the pix.
I'm not sure if I made that clear or not. You won't need to have any "no" commands in your config. The only time where you might need to use it is to remove something that didn't overwrite the old value, but instead made another one. IE:
ip address 192.168.1.2
ip address 192.168.2.2
If I were changing the ip to 192.168.2.2 that is most likely what would happen when I type the command. To fix this I'll type "no ip address 192.168.1.2" and it will remove the old ip. Another common use for no is when you have a port that is disabled. You can type "no shut" and it will enable the port.