No, you can't.  You'll have to create a new schema, then recreate and reload your tables in the new schema (can't move tables, either).  I just had to do this all myself.

A place I look for information like this is the REST API, which is used by the UI, CLI and SDK.  If you look at "Update a schema" you'll see there is no option for storage_root: https://docs.databricks.com/api/azure/workspace/schemas/update