The API could let you do this. What policies are you trying to update? Group Policies? and are you trying to edit an existing policy or create a new one?
if you are just creating a new one you can use this one and use this one. You would put the template id in place of the network id.
https://developer.cisco.com/meraki/api-v1/create-network-group-policy/
Editing in bulk could be harder.
I can try to address the basic steps if necessary.
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