Is it possible to set a specific directory as read only? i.e. prevent the user from uploading images (or indeed files for MCFileManager) to a specified directory or deleting files from that directory? I've been through the manual, forum and examined the config options, but can't see anyway of doing this. Something like the following

$mcImageManagerConfig['filesystem.readonly_directory_pattern'] = '/^somedirectory$/i';

I want to deliver a set of icons (the silk icon set) with the install for my CMS and don't want to the user to be able to upload any other files to the directories containing these icons or indeed delete any of them.