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:
$mcFileManagerConfig['createdir.allow_override'] = "include_file_pattern";
Example of usage in a mc_access file:
# Override something
createdir.include_file_pattern=/^onlythis$|^onlythat$/i
# Allow override
createdir.allow_override=include_file_pattern