State regulators said yesterday that they will probably change the complex formula they use to determine how many Massachusetts residents face a tax penalty for not having health insurance, because spiraling costs are making coverage unaffordable for too many people. Each year, the Massachusetts Health Insurance Connector Authority board updates the formula it uses to determine whether health insurance is affordable for individuals, couples, and families and whether people in each group should face a tax penalty for not having coverage. The state’s landmark 2006 health law requires nearly everyone to have health insurance or to pay a stiff tax...