A nomination to a spouse is not automatically revoked on divorce or re-marriage;
Beneficiaries are limited to SIS dependants or your estate – although you can effectively get around this by also having in place a Will containing a Testamentary Discretionary Trust and directing your super death benefit to your estate as the final “fall-back” beneficiary after exhausting all living SIS dependants;
Potentially could be amended or revoked by your attorney under an enduring power of attorney – unless you insert a restriction in the instrument granting the power or even specifying this restriction in the SMSF trust deed.
Note – that it is good practice to ensure that you specify what will happen in the event that any conditions that are imposed in the BDBN are not satisfied.