Gareth,
There is no simple way to bulk update permissions. There are APIs to manage users and permissions and if you have API skills it would be possible to create a script that could find the users for each space and then update permissions.
Best practice is to use User Groups and to provide access via the groups rather than through individual userids. In many organizations the ability to create spaces is limited to Administrators or a Space Curation user(s).
If you would like to investigate the API option please respond here.
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Mark Ketteman
Digital Business Solutions Engineer
IBM United Kingdom Limited
London
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