There is an option to update users:
Update Network Meraki Auth User
Operation Id:updateNetworkMerakiAuthUser
Description:Update a user configured with Meraki Authentication (currently, 802.1X RADIUS, splash guest, and client VPN users can be updated)
PUT /networks/{networkId}/merakiAuthUsers/{merakiAuthUserId}
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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