Below the list of shares on the first page is a button which will make the current configuration active. This is done by stopping and starting the running NFS server processes.
If some directory and one of its sub-directories is exported, the options for the most specific directory will apply to clients. For example, if /usr and /usr/local are both exported, a client accessing /usr/local/bin will be effected by the options for the /usr/local export.