Disable that users overwrite global album settings

I would like to configure my Gallery2 Installation in a way that the "Matrix" Theme is the Theme for all newly created albums. How can I achieve this?
I have selected Matrix in the General Settings, and I have set Matrix as the Theme of the "root" album. So the default value for all sub-albums is Matrix, but this can be overwritten by the user. How can I prevent this?
(the same problem applies for other album settings, like maximum image size).

Gallery version: 2.2.3
PHP version (e.g. 5.1.6): 4
Webserver: Apache 2.2.4
Database: MYSQL 5.0.41
Activated toolkits: GD
Operating system: Unix
Browser: IE7