It is not possible to change permissions for the owner of a personal space. No error is thrown, the changes just are not made. If another administrator is specified there should be no reason why the permissions cannot be changed.
The above two points are the reason why I have logged this as a bug report rather than a feature request - the functionality is there, it just isn't working for personal spaces as it does for global spaces.
This should be resolved to cater for the following scenarios amongst others:
- Administrators could use personal spaces to track information about a user but not want that user to have access to it (for example HR could keep an electronic employee file, etc)
- You might want to allow users control over most content/etc but be able to restrict certain portions of their personal space (for example making the Home page read-only and using it to track user details, etc)