This Medigap Open Enrollment Period could be a one-time enrollment chance after you have reached 65 or older and first enroll in Medicare Part B. If you identify that a Medicare Supplement plan isn't right for you now and choose to use it later, you'll be turned down for coverage. You’d undergo a process called underwriting to see if you're acceptable to the insurance firm.
Typically, though, you may want to get a Medicare Supplement plan during the one-time Medigap Open Enrollment Period to take advantage of the guaranteed concern. You shouldn't worry about qualifying for coverage.