Yes. Simply use Additional Coverage to add a spouse or child. Just be sure to only complete the ‘Statement of Physical Condition’ section for the Dependent who’s being added and not for anyone who is already covered.
Additionally, a spouse can be covered for more insurance as an Associate Member and, usually, for considerably less. Unless a spouse is 10 or more years older than the Member, in which case, it would be more cost effective to have a spouse covered as a Dependent.