Two options.
Option 1 - Clone the MX68 network and place the MX75 (or whatever MX you move to) in the new network. It will copy all of the config over
Option 2 - Remove the MX68 from the network (with the remove button on the MX page) and then add the MXxx back to this network and it will assume all settings.
The couple of exceptions I can think of that get reset when you do either option is making sure the LAN port mapping aligns as MX models can have different LAN port counts. https://documentation.meraki.com/MX/Other_Topics/MX_Cold_Swap_Replacing_an_Existing_MX_with_a_Differ...
And, if you have site to site VPN configured I believe it resets back to disabled when you remove a MX from a network or clone a MX network. So, just reenable S2S VPN if needed.
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