Rules for making mid-year plan design changes

[Guest TamraCS]

We have a self-insured prescription plan and are considering raising the copayments mid-year. The prescription plan is the same regardless of which health plan election the employees choose during open enrollment. If we raise the copayment structure, can we do a 'one-way' enrollment period in which we allow employees to opt out of our health plan in order to enroll in a spouse's plan? In addition, if we make a plan design change on the health plans that includes increase of copayment, would we have to allow an open enrollment period for employees to switch plans? And one more... what are the rules for mid-year design changes? How much notice must be given, etc.