As above ^ shoot for the straight swap out. I had no issues swapping an MX64 over to an MX75.
Configure the new device offline, WAN IP, DNS via local status page. Remove the old Mx from network and move the new one in.
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.