How to set permissions for root workspace objects (e.g. repos)?

[andy-potter-evotix]

Via the Databricks SDK we can successfully set permissions on specific workspace objects (e.g. clusters, jobs, notebooks, etc). However, when it comes to repos we want to be able to set a permission at the root level (i.e. for all repos) in a workspace. The documentation for the permission set/update methods in the SDK (and the API guide) says that objects inherit permissions from the root object. But there doesn't appear to be a way to set the root object level permissions. Is this something that is not possible via the API/SDK at the moment?