I’ve just completed the same process for my home lab. Replacing an MX68 with another MX device.
As you state, remove the old device from your Network and replace with the new. You’ll have to preconfigure the new devices Internet port IP details (unless you’re assigning via DHCP).
Youll only lose internet connectivity during the process of physically swapping the devices over
Darren OConnor | doconnor@resalire.co.uk
https://www.linkedin.com/in/darrenoconnor/
I'm not an employee of Cisco/Meraki. My posts are based on Meraki best practice and what has worked for me in the field.