Premium-only plans were designed to provide employers with a means to offer pre-tax premiums for specific welfare benefits.
The Internal Revenue Code Section 125 specifically outlines where pre-tax deductions are applicable. Favorable tax treatment requires that Section 125 imposes certain limitations on when plan/benefits may be changed; otherwise, elections must remain in effect for the plan year. “Change in family status” is considered a circumstances for which a change can be made to your Section 125 election (there are alternative triggers; make sure to check with your employer to see which qualify).
Most welfare plans require a written Summary Plan Description (SPD) and/or plan document. Generally, it would make more sense to incorporate the cafeteria plan provisions within the SPD/Plan Document since these provisions are generally specific to each welfare plan. Some employers may consider a “wrap plan” that includes both SPD and the Section 125 cafeteria plan provisions combined into a single document. This would provider a simpler approach to the administration of plan benefits and/or provisions.