Currently there are only Save Category and Save Category Value permissions for the roles.
if you hover over the "Save Category/Save Category Value" permission you will see the following text:

"Create, edit, and delete test artifact categories from within a test artifact or on the Manage Project Properties page.  Only project administrators and users with JazzProjectAdmins or JazzAdmins repository permissions can access the Manage Project Properties page.  To create, edit, and delete test artifact categories on the Manage Project Properties page, you must also have permission to save administrative options."

In Save Category permission, there is Global > Create and Promote sub permissions.
If you want to restrict the user to be able to do something on local category but not global category,
other than creating and promoting category, you can not really distinguish them. For existing global categories, even though there are no create and promote permissions, the user may still edit or add new values to it. I guess it would be good to have Global > Edit permission to control the user Not able to update any existing global categories which is missing in RQM currently.