An unmarried person living in a community property state has an IRA naming his three adult children as beneficiaries. Then he marries, a year later he dies without changing the beneficiary designation. Can the beneficiary designation be undone by the surviving spouse? Is there a requirement that the IRA owner change the IRA beneficiary designation upon marriage? Does it matter that although its a community property state, all contributions were separate property as they were made prior to marriage?

CP applies to property acquired during the marriage, not before. There is no spousal consent requirement for distributions of an IRA which consists of separate property. You should check to see if earnings that accrue on the IRA after marriage would be CP.