You are automatically registered in a group insurance plan. However, you can opt-out from the plan at no cost if you do so during the amendment period.
There are only one kind of opting-out:
An annual withdrawal means that you are excluded from the insurance plan for the year. Therefore, you will be automatically reinstated the next year if you register as a student. You will then have to withdraw again, if you wish, during the amendment period.
If you wish to withdraw from the plan, you must do so during the amendment period which is between February 1st and February 20th.