You should be able to use dd on the first to copy the desired /dev/mtd# to /tmp, then scp to download it.
You can then use scp to copy that file to the second device and
mtd write file partition-name it.
Potentially you should do this one at a time and
rm the finished file from /tmp before doing another.
If you are unsure on the partition numbered device names (as needed by
dd) vs their mtd names, as needed by
mtd write you can get a list with
Keep in mind that one partition stores unit-unique information like the MAC address, you do not want to clone or overwrite that.
You'll need to decide if you want to be cloning the writeable filesystem partition or not. Depending on what changes you are trying to capture, that could potentially be the only think you want to clone; it's possible though that there will be unit-unique things in there that should not be cloned (ssh keys, wifi SSID and password, anything derived from MAC address, etc). You're stepping outside the realm of intended one-off usage so may have to invent your own process.
The binary compiled "sketch" of any program loaded into the ATmega would need to be handled via Arduino-type methods, either finding a way to read it back out (perhaps via ISP), or better building it to generate the hex file and distributing that.
Keep in mind that in distributing binaries you likely incur GPL obligations you will need to be prepared to meet.