Changing Metadata with the automation API

Hello,
I'd like to update the metadata for the assets using the Automation API. It seems that not all metadata fields can be modified directly via the API.
Where can I find these restrictions?
Using `/automation/v1.0/metadata/templates/default/fields`, you can see all fields, including those that cannot be modified.
Furthermore, it’s not possible to retrieve the values of a list, such as for `default.theme`.