possible, but tricky. you have to make sure that your feed is in sync on the devices before you publish a message from any of them, or else you could fork your feed, which is difficult to recover from.

another option is to copy the key, but only run a scuttlebot server on one device; from the other device you can connect to the server by setting the environmental variable ssb_host to the remote ip address while running your ssb client. there is some rpc overhead to this approach.

the safer and simpler option is to use a different key on each of your devices.