Please remember when doing anything where you may lose sync or need to disconnect/swap follow this procedure -
Login to the modem/router interface and click on the "Disconnect" button - this terminates the "ppp" session to the ISP (not sync to the exchange).  Wait a good minute after the button changes to "Connect" (refresh the page to be sure).
Then power down the modem/router. Wait a good minute before unplugging the modem/router or it's filter from the line. Then swap whatever needs to be swapped.
Wait another 10 minutes before powering up again.