Allow modules to alter the default content_access settings based on a specific node.

I want to try to set the default node permissions based on a property of that node on my website. A 'meeting' node for the department 'management' should be by default not accessible for anonymous users, while the meetings for other departments should. Editors in my system do not have content_access permissions (and that's for their own protection!) so I need to provide an automatical solution.

I found that content_access lacks good hooks in general, and it does not provide any way of doing what I need.

I think that this would be perfectly possible if content_access_per_node_setting would use a content_access_get_default_node_settings($op, $node) instead of content_access_get_settings() directly.
Then in that new function a drupal_alter hook can be implemented, which in turn can be used to change the default permissions based on the properties of the specific node.

I see only advantages of this change. When node-specific content access settings are enabled, and the admin screen with content access settings for a specific node is loaded, these defaults will be shown and can be manually edited. Otherwise the altered settings will be used.

I've tested the changes manually but don't know how I can test the drupal_alter in the test cases. I would need to add a module, solely for testing purposes. It should not be installable as a normal module. Does anyone know how to do that?