You can spin up a new Meraki organization for the subscription-licensed networks and keep your existing org on co-term until you're ready to fully migrate.
This approach avoids breaking compliance and lets you phase the migration over time.
If your environment is large enough, Cisco sometimes offers Enterprise Agreements (EA) that allow flexible licensing pools.
I am not a Cisco Meraki employee. My suggestions are based on documentation of Meraki best practices and day-to-day experience.
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