You can try out using a MetaDataExtender class, and register it in an initialization module like:

MetaDataExtenderClass

public class PageTypeMetaDataExtender : IMetadataExtender
    {
        public void ModifyMetadata(ExtendedMetadata metadata, IEnumerable<Attribute> attributes)
        {
        }
    }

    And the initialization

MetadataHandlerRegistry registry = context.Locate.Advanced.GetInstance<MetadataHandlerRegistry>();
            registry.RegisterMetadataHandler(typeof(ContentData), new PageTypeMetaDataExtender());

    Of course you could create an extender for each page type, or use the contentdata approach i've shown here.  Or get fancy and use attributes and read them from the type of the contentdata coming across.  Inside the modifymetadata method you can check out the properties on each page from the metadata and set their status to read only or something similar (i don't know if there's a way to set it to disabled specifcally, but you can probably hide or set to read only) on specific conditions.

Hope this helps!