I think your best option is using the API to create the alert profile(s) for Networks across an Org.
https://developer.cisco.com/meraki/api-v1/create-network-sensor-alerts-profile/
Or, and this one really depends what already exists, but you can clone unbound Networks which would copy any Sensor Alert Profiles in them. Then you can bind the cloned Network to a template and the Alert Profiles are retained. You'd still need to associate the Alert Profiles with the Network specific Sensors.
If all these Networks are already created and bound to the template I think it goes back to API being the only mass create option.
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