Is there a way in the GUI to set permissions on multiple Categories at once or will it require Core Service code (example)?
I have to set about 40+ to set to all the same permission-set.
AFAIK, there is no straight forward way to do so in GUI, you may need to write a Core Service code for it.
There is no way to do this in the standard GUI, however, please see my blog article on the subject, where I show how to do this from a relatively straightforward Powershell script.
With some boilerplate code in place, the script to set permissions on a category ends up looking like this:
$catPermsTest = $core.Read("/webdav/01%20Definitions/PermsTest", $defaultReadOptions) addPermissions $group $catPermsTest Read