This option should contain a comma separated list of options you can override. These options can then be changed specifically in various directories by adding them to a mc_access file. The default value of this option is "*" which tells TinyMCE to allow override of all options.
Example of usage in the config.php file
$mcFileManagerConfig['createdir.allow_override'] = "include_file_pattern";
Example of usage in the Web.Config file
<add key="createdir.allow_override" value="include_file_pattern" />
Example of usage in a mc_access file
# Override something createdir.include_file_pattern=/^onlythis$|^onlythat$/i # Allow override createdir.allow_override=include_file_pattern